tests: extend fuzz parser coverage

[BeaCox]

Summary:

• add a LYB data parser fuzz target that preserves binary input length via fd-backed parsing
• add a schema-mount XML data parser fuzz target with runtime extension data and a non-crashing seed
• allow fuzz targets to build without the unit-test/CMocka dependency and make LibFuzzer targets link sanitizer runtimes correctly
• avoid terminating the fuzzer process from existing harness setup/allocation failures

Testing:

• cmake -S . -B build-fuzz-check -G Ninja -DENABLE_TESTS=OFF -DENABLE_FUZZ_TARGETS=ON -DFUZZER=AFL -DCMAKE_BUILD_TYPE=Debug
• cmake --build build-fuzz-check --target lys_parse_mem_fuzz_harness lyd_parse_mem_xml_fuzz_harness lyd_parse_mem_json_fuzz_harness yang_parse_module_fuzz_harness lyd_parse_lyb_fuzz_harness lyd_parse_schema_mount_xml_fuzz_harness -j2
• ./build-fuzz-check/lyd_parse_schema_mount_xml_fuzz_harness < tests/fuzz/corpus/lyd_parse_schema_mount_xml/valid-mounted-leaf
• cmake -S . -B build-fuzz-libfuzzer -G Ninja -DENABLE_TESTS=OFF -DENABLE_FUZZ_TARGETS=ON -DFUZZER=LibFuzzer -DCMAKE_C_COMPILER=clang -DCMAKE_BUILD_TYPE=Release
• cmake --build build-fuzz-libfuzzer --target lyd_parse_lyb_fuzz_harness lyd_parse_schema_mount_xml_fuzz_harness -j2
• ASAN_OPTIONS=detect_leaks=0 ./build-fuzz-libfuzzer/lyd_parse_schema_mount_xml_fuzz_harness -runs=1 tests/fuzz/corpus/lyd_parse_schema_mount_xml/valid-mounted-leaf

[michalvasko]

Okay, no problem, thanks.