fix codec logic and failure handling

[edsiper]

Summary

• preserve OTLP dictionary-backed attributes and profile metadata during encoding
• balance MessagePack containers and reject integer conversions that would wrap or truncate
• fix text encoding of empty arrays
• make OTLP and profile allocation-failure cleanup atomic, including empty collection handling
• add regression coverage for wire metadata, attribute indexes, malformed integers, and empty inputs

Root cause

Several codec paths relied on unchecked conversion or allocator behavior. The OTLP dictionary builder did not construct the attribute table or copy profile metadata, MessagePack maps were not closed when MPack tracking was enabled, and multiple failure paths either lost ownership or cleaned up dangling pointers.

Validation

• ./scripts/agent-verify.sh
• GCC build and all four CTest executables
• Clang debug build and all four CTest executables
• MPack DEBUG tracking build and all four CTest executables
• Valgrind full leak check of cprof-test-opentelemetry_transcoder
• GCC -fanalyzer; no project-source diagnostics remain (vendored CFL/MPack diagnostics only)

An AddressSanitizer build completed, but its existing test binaries hung at their first test without emitting a sanitizer diagnostic, so ASan results are not claimed here.

Compatibility

No public C structure layouts or function signatures change. OTLP output now includes fields that were previously dropped and valid dictionary entries for existing attribute references. Malformed MessagePack integers that previously wrapped or truncated are now rejected.