fix(h3): preserve pooled request trace context

[EdmondDantes]

Pooled HTTP/3 routes requests to a worker before the in-thread trace-context parser runs, leaving handler getters and access records without trace or span IDs. Prepare trace context, response compression and the JSON default through one shared helper in HTTP/1, HTTP/2, HTTP/3 and worker dispatch, using the dispatch thread's configuration. Preserve early H1/H2 parsing for WebSocket upgrades and avoid retaining valid trace headers twice.

Share the JSON-default response stub across parser/session unit tests and add an aborting stub for parser fuzz harnesses, which link the protocol helper without the response implementation.

Add a pooled HTTP/3 regression test that checks handler getters and access-log TraceId/SpanId for sampled and unsampled valid headers, uppercase and zero-ID headers, missing headers, and disabled telemetry.

Validation:

• make -j4 passes.

• The new test reproduces missing IDs on the previous module and passes after the fix, both with the reactor pool and with a temporary single-worker, pool-disabled variant.

• Related HTTP/1 and HTTP/2 compression, HTTP/3 pool compression, JSON, trace-context and access-duration PHPT tests pass.

• Rebuilt on current main and reran the regression and four related PHPT tests: all pass.

• All 22 cmocka/CTest targets pass. Both HTTP/1 and HTTP/2 fuzz harnesses build and complete 100 seeded smoke iterations under ASan/UBSan.

Fixes #352.

[github-actions]

Coverage

Total lines: 84.60% → 84.66% (+0.06 pp)

File	Baseline	Current	Δ	Touched
src/core/http_connection.c	83.67%	83.63%	-0.04 pp	●
src/core/http_protocol_handlers.c	89.01%	89.80%	+0.78 pp	●
src/core/worker_dispatch.c	83.50%	83.45%	-0.04 pp	●
src/http2/http2_strategy.c	85.89%	85.85%	-0.04 pp	●
src/http3/http3_dispatch.c	88.30%	88.37%	+0.07 pp	●
src/http3/http3_listener.c	77.96%	77.66%	-0.30 pp
src/http_request.c	85.76%	86.25%	+0.49 pp
src/log/http_log.c	69.29%	70.45%	+1.16 pp