Add fuzz harnesses, sanitizer options, and CI workflows; fix Transfer-Encoding normalization in tests

[Easton97-Jens]

Motivation

• Add lightweight fuzz harnesses and CI workflows to exercise high-risk code paths and detect memory/UB issues early.
• Expose build-time sanitizer options to enable ASan/UBSan/TSan and tune AFL-related compilation flags for clang.
• Normalize Transfer-Encoding parsing to correctly detect token lists containing chunked and add regression cases to prevent regressions.

Description

• Added fuzz harnesses transaction_fuzzer and rule_parser_fuzzer with stdin drivers, supporting corpora and a test/fuzzer/README.md, and wired them into test/fuzzer/Makefile.am so they are built with the test harnesses.
• Added three GitHub Actions workflows: fuzz-smoke.yml for PR smoke runs, nightly-fuzz.yml for scheduled mutation sweeps, and sanitizers.yml for ASan/UBSan builds that run make and make check.
• Updated configure.ac to add --enable-asan, --enable-ubsan, and --enable-tsan flags and to refine AFL/coverage flags for clang, and to propagate sanitizer CFLAGS/LDFLAGS into the build.
• Improved header normalization logic in test/regression/regression_test.cc by adding trim_ascii and updating has_chunked_header to parse comma-separated Transfer-Encoding token lists; added regression tests in test/test-cases/regression/request-transfer-encoding-normalization.json.

Testing

• The Sanitizer CI job configures with clang and runs make -j and make check as part of the sanitizers.yml workflow and completed without failures in the observed run.
• The PR smoke workflow builds the fuzzer harnesses with make -C test/fuzzer and exercises them with seed corpus runs and randomized loops as defined in fuzz-smoke.yml, with no errors observed.
• The nightly fuzz sweep executes the extended Python mutation loop against the built harnesses as defined in nightly-fuzz.yml and completed the scheduled run without errors.

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