Log malformed HTTP/2 requests

[bneradt]

Unlike HTTP/1 transactions, malformed HTTP/2 requests are rejected before HttpSM creation, so they bypassed the normal transaction logging path. That left malformed h2 traffic out of squid.log even when similar h1 failures were visible.

This adds a pre-transaction LogAccess path for malformed h2 request headers and emits a best-effort access log entry before resetting the stream.

[Copilot]

Pull request overview

This PR adds a “pre-transaction” access logging path for malformed HTTP/2 request headers that are rejected before HttpSM is created, so these failures can still be recorded in squid.log (similar to HTTP/1 behavior).

Changes:

• Add LogAccess::PreTransactionLogData and extend LogAccess to support access log marshaling without an HttpSM.
• Emit a best-effort access log entry from the HTTP/2 layer when rejecting malformed HEADERS/CONTINUATION input.
• Add gold and unit tests validating both malformed and valid HTTP/2 request logging.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/gold_tests/connect/replays/h2_malformed_request_logging.replay.yaml	Adds replay traffic for valid HTTP/2 GET and CONNECT cases used by the gold test.
tests/gold_tests/connect/malformed_h2_request_client.py	Adds a low-level client to send deliberately malformed HTTP/2 requests on the wire.
tests/gold_tests/connect/h2_malformed_request_logging.test.py	Adds an integration test that asserts malformed HTTP/2 requests are access logged and do not reach origin.
src/proxy/logging/unit-tests/test_LogAccess.cc	Adds Catch2 unit tests covering pre-transaction LogAccess marshaling behavior.
src/proxy/logging/LogAccess.cc	Implements pre-transaction initialization and adds guards/fallbacks for marshaling without HttpSM.
src/proxy/logging/CMakeLists.txt	Registers the new test_LogAccess executable in CMake when testing is enabled.
src/proxy/http2/Http2ConnectionState.cc	Logs malformed decoded request headers via Log::access() before stream reset/GOAWAY.
include/proxy/logging/LogAccess.h	Defines PreTransactionLogData and adds support helpers for pre-transaction logging mode.
include/proxy/http2/Http2Stream.h	Exposes a const accessor for the decoded receive header (get_receive_header()).