Make the SemanticLogger session request/coroutine-scoped for concurrent runtimes

[koriym]

Context

The cache observability layer (#178) binds SemanticLoggerInterface (SafeSemanticLogger) as a process singleton with a stack-based session (open / event / close + depth). This matches the pre-existing 1.x logger binding (also a singleton).

Problem

Under concurrent long-running runtimes (Swoole / RoadRunner coroutines sharing one worker process), concurrent requests share the single logger instance. An interleaved open / close violates the LIFO stack, SafeSemanticLogger marks the session broken, and the current request's log is dropped (empty flush) — not merely interleaved.

• Cache behavior is unaffected — logging is a best-effort side-channel that never breaks cache reads/writes.
• The default PHP-FPM deployment (one request per process) is completely unaffected.
• Documented as a Known Limitation in tests/CACHE_DEPENDENCY_TESTS.md.

Proposed fix

Make the logger request/coroutine-scoped instead of a process singleton:

• bind SemanticLoggerInterface in a request/coroutine scope, or
• keep a singleton facade that delegates to a per-request session resolved from the host request context.

This is tied to the host flush-lifecycle (the package delegates request-end flush to the host transfer layer), so it should be designed together with the host integration.

Acceptance criteria

• Interleaved concurrent A/B logging test proving logs cannot cross-nest or be dropped.
• Per-request/coroutine session lifecycle integrated with the host flush boundary.

References

• Rebuild cache observability on Koriym.SemanticLogger #178 (cache observability on Koriym.SemanticLogger)
• src/Log/SafeSemanticLogger.php, src/Log/SafeSemanticLoggerProvider.php, src/DonutCacheModule.php