[Better Tests] Add tests for coverage-guided fuzz targets

[IvanBM18]

WIP: Created just in case im asked to add unit tests for the fake blackbox fuzzer, else this one will be closed

Bug: b/555386435

Overview

Before wiring the coverage-guided fuzz targets into full end-to-end fuzz_task integration suites, we want fast standalone tests confirming each binary's exit code, AddressSanitizer crash signature, crash-* artifact generation, and alignment with ClusterFuzz's constants.RUNS_TO_REPRODUCE threshold.

To run the tests use:

pytest test_suites/data/fuzzer/coverage_guided/coverage_guided_test.py

Note: this ones doesn't require to import src/third_party since they are not testing CF code :D

Changes

• Add test_suites/data/fuzzer/coverage_guided/coverage_guided_test.py (TestCoverageGuidedFuzzers) to verify the behavior of the coverage-guided fuzz targets:
• Add test_suites/data/fuzzer/coverage_guided/__init__.py for test discovery and lint compliance.