refactor(Scripts): extract Xcode report policy

[kyleve]

Summary

• move embedded Python out of test, profile, and flaky into importable modules under Tools/
• share schema-tolerant xcresult traversal and snapshot reporting while keeping each command's policy separate
• retain public Bash argument parsing, simulator/process orchestration, streaming output, and legacy exit behavior
• add fake-Xcode public-command contracts for argv/environment, stream/status propagation, malformed results, interruption, and closed pipes

Why

The high-risk untested surface was structured parsing and reporting policy, not the public shell bootstrap. Extracting those pieces provides direct tests and reuse without recreating the discarded Swift command framework.

Design decisions

• xcode_results.py owns xcresult traversal only; it does not invoke processes.
• snapshot_reports.py is shared by test and profile; thresholds and failure semantics remain command-specific.
• test_runner.py, profile_results.py, and flaky_results.py stay separate so affected-scope, profiling, and flake policies cannot blur together.
• ./test keeps TTY redraws, captured-CI heartbeats, cached denominators, image progress, and zero-test failure.

Compatibility

Public paths, flags, scope-selector precedence, output streams, defaults, and exit policies match main.

Adversarial coverage

• Xcode failure through pipelines; progress/tee failure after Xcode success
• zero-test success refusal, invalid bytes, high-volume output, and unlaunchable executables
• schema-shifted/truncated xcresult JSON, unknown nodes, parameterized names, and missing fields
• profile parser failure warns after a valid run; build/test failure remains fatal
• flaky test failures become observations; infrastructure/build failures remain fatal
• Ctrl-C reaches the active Xcode child; a closed output pipe does not leave it running
• mutations for zero-test success, lost child status, ignored progress failure, and trusted malformed roots are all killed

Testing

• 62 Python tests
• 15 retained Ruby tests / 212 assertions at this layer
• ./test StuffCoreTests (real Xcode smoke, passed)
• ./profile --tests-only --no-snapshots (2,119 tests parsed, passed at stack tip)
• ./flaky --suite-runs 1 --iterations 2 --no-update (2,120 tests observed, passed at stack tip)
• full retained-tool, ShellCheck, formatting, attribution, and shard-plan gates

Stack

Second PR; based on #283.

[kyleve]

Review focus: this deliberately preserves the shell implementation’s fail-closed bundle floor instead of introducing a new target catalog in this extraction. The direct tests cover both rejection and dependency closure; a later manifest-format change must keep under-selection observable.