refactor: extract route_table collaborator from webserver_impl

C-4 of the webserver_impl god-object decomposition. Move the v2 3-tier
route table (exact / radix / regex) and its LRU cache front-end out of
detail::webserver_impl into a dedicated detail::route_table collaborator.

route_table owns route_table_mutex_, the three tiers (exact_routes_,
param_and_prefix_routes_, regex_routes_ + the nested regex_route struct),
route_lru_cache, the tier_hit / lookup_result types, and the routing
primitives: the lookup pipeline (lookup_v2 + canonicalize_lookup_path),
invalidate_route_cache, register_v2_route, and the locked upsert/reject
family (find_v2_entry_by_path_, upsert_v2_table_entry_locked_ and its
sub-helpers, reject_terminus_collision, reject_duplicate_v2_entry_).

Lock ownership stays with the orchestrator (scoped-lock design): the
on_*/route registration sequence in webserver::on_methods_ holds
routes_.lock_for_write() across the conflict probe + table mutation, and
the lambda_resource shim-creation POLICY (prepare_or_create_lambda_shim /
commit_handlers_to_shim) stays on webserver_impl -- only the containers,
the lookup, and the locked table primitives moved. register/unregister
sweep the tiers directly under lock_for_write() (route_table members are
public, matching the webserver_impl / hook_bus stance). The
table-before-cache lock order is now an internal invariant of route_table.

webserver_impl keeps thin lookup_v2 / invalidate_route_cache forwarders
plus tier_hit / lookup_result type aliases, so every dispatch call site
and all ~8 white-box routing test/bench files compile unchanged.
resolve_resource_for_request stays on webserver_impl as dispatch glue
(applies captured params to the request, sets matched_path_template).

New files: src/httpserver/detail/route_table.hpp + src/detail/route_table.cpp.
Build clean; 109/109 tests PASS; file-size gate PASS.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: etr

src/Makefile.am

@@ -25,11 +25,11 @@ lib_LTLIBRARIES = libhttpserver.la
 # builds. The WS-off branch in websocket_handler.cpp provides stub
 # definitions (every member throws feature_unavailable except is_valid()
 # which returns false).
-libhttpserver_la_SOURCES = string_utilities.cpp webserver.cpp webserver_add_hook.cpp http_utils.cpp file_info.cpp http_request.cpp http_request_auth.cpp http_response.cpp http_response_factories.cpp http_resource.cpp create_webserver.cpp create_test_request.cpp websocket_handler.cpp hook_handle.cpp peer_address.cpp resource_hook_table.cpp cookie.cpp detail/http_endpoint.cpp detail/body.cpp detail/ip_representation.cpp detail/ip_access_control.cpp detail/ws_registry.cpp detail/hook_bus.cpp detail/http_request_impl.cpp detail/http_request_impl_args.cpp detail/http_request_impl_tls.cpp detail/webserver_lifecycle.cpp detail/webserver_register.cpp detail/webserver_routes.cpp detail/webserver_routes_upsert.cpp detail/webserver_callbacks.cpp detail/webserver_callbacks_lifecycle.cpp detail/webserver_websocket.cpp detail/webserver_dispatch.cpp detail/webserver_request.cpp detail/webserver_response_queue.cpp detail/webserver_body_pipeline.cpp detail/webserver_error_pages.cpp detail/webserver_aliases.cpp detail/webserver_hook_firing.cpp detail/hook_phase_dispatch.cpp
+libhttpserver_la_SOURCES = string_utilities.cpp webserver.cpp webserver_add_hook.cpp http_utils.cpp file_info.cpp http_request.cpp http_request_auth.cpp http_response.cpp http_response_factories.cpp http_resource.cpp create_webserver.cpp create_test_request.cpp websocket_handler.cpp hook_handle.cpp peer_address.cpp resource_hook_table.cpp cookie.cpp detail/http_endpoint.cpp detail/body.cpp detail/ip_representation.cpp detail/ip_access_control.cpp detail/ws_registry.cpp detail/hook_bus.cpp detail/route_table.cpp detail/http_request_impl.cpp detail/http_request_impl_args.cpp detail/http_request_impl_tls.cpp detail/webserver_lifecycle.cpp detail/webserver_register.cpp detail/webserver_routes.cpp detail/webserver_routes_upsert.cpp detail/webserver_callbacks.cpp detail/webserver_callbacks_lifecycle.cpp detail/webserver_websocket.cpp detail/webserver_dispatch.cpp detail/webserver_request.cpp detail/webserver_response_queue.cpp detail/webserver_body_pipeline.cpp detail/webserver_error_pages.cpp detail/webserver_aliases.cpp detail/webserver_hook_firing.cpp detail/hook_phase_dispatch.cpp
 # noinst_HEADERS: shipped in the tarball but NEVER installed under $prefix/include.
 # Detail headers (httpserver/detail/*.hpp) live here so they cannot leak to
 # downstream consumers — the public surface comes in through <httpserver.hpp>.
-noinst_HEADERS = httpserver/string_utilities.hpp httpserver/detail/modded_request.hpp httpserver/detail/http_endpoint.hpp httpserver/detail/body.hpp httpserver/detail/webserver_impl.hpp httpserver/detail/webserver_impl_dispatch.hpp httpserver/detail/connection_state.hpp httpserver/detail/ip_access_control.hpp httpserver/detail/ws_registry.hpp httpserver/detail/hook_bus.hpp httpserver/detail/secure_zero.hpp httpserver/detail/http_request_impl.hpp httpserver/detail/resource_hook_table.hpp httpserver/detail/route_entry.hpp httpserver/detail/lambda_resource.hpp httpserver/detail/segment_trie.hpp httpserver/detail/route_cache.hpp httpserver/detail/route_tier.hpp httpserver/detail/unescape_helpers.hpp gettext.h
+noinst_HEADERS = httpserver/string_utilities.hpp httpserver/detail/modded_request.hpp httpserver/detail/http_endpoint.hpp httpserver/detail/body.hpp httpserver/detail/webserver_impl.hpp httpserver/detail/webserver_impl_dispatch.hpp httpserver/detail/connection_state.hpp httpserver/detail/ip_access_control.hpp httpserver/detail/ws_registry.hpp httpserver/detail/hook_bus.hpp httpserver/detail/route_table.hpp httpserver/detail/secure_zero.hpp httpserver/detail/http_request_impl.hpp httpserver/detail/resource_hook_table.hpp httpserver/detail/route_entry.hpp httpserver/detail/lambda_resource.hpp httpserver/detail/segment_trie.hpp httpserver/detail/route_cache.hpp httpserver/detail/route_tier.hpp httpserver/detail/unescape_helpers.hpp gettext.h
 nobase_include_HEADERS = httpserver.hpp httpserver/body_kind.hpp httpserver/cookie.hpp httpserver/constants.hpp httpserver/create_webserver.hpp httpserver/create_webserver_setters.hpp httpserver/create_test_request.hpp httpserver/webserver.hpp httpserver/webserver_routes.hpp httpserver/webserver_runtime.hpp httpserver/webserver_websocket.hpp httpserver/webserver_hooks.hpp httpserver/websocket_handler.hpp httpserver/http_utils.hpp httpserver/http_utils_helpers.hpp httpserver/ip_representation.hpp httpserver/file_info.hpp httpserver/http_request.hpp httpserver/http_response.hpp httpserver/http_resource.hpp httpserver/feature_unavailable.hpp httpserver/iovec_entry.hpp httpserver/http_arg_value.hpp httpserver/http_method.hpp httpserver/hook_phase.hpp httpserver/hook_action.hpp httpserver/hook_handle.hpp httpserver/hook_context.hpp
 
 AM_CXXFLAGS += -fPIC -Wall