test: add synthetic NTFS record fixtures, sanitizers, and parser fuzzing

[daniyusk]

Summary

Adds synthetic NTFS test fixtures, parser hardening, ASan/UBSan CI integration, and an opt-in libFuzzer target for MftRecordParser.

Changes

• Synthetic fixtures infrastructure (tests/NtfsFixtures.hpp, tests/NtfsFixtures.cpp):
  • Valid and truncated FILE records.
  • Valid and corrupt update sequence array (USA) fixups.
  • Resident and non-resident data attributes.
  • Positive, negative, and sparse data runs with arithmetic encoding.
  • Malformed attribute offsets and sizes.
  • UTF-16 records with unpaired surrogates.
  • Sanitized filename collision fixtures.
• Parser regressions and hardening:
  • Added arithmetic overflow protection (checked_add) in src/MftRecord.cpp.
  • Added invalid UTF-16 surrogate handling with U+FFFD replacement in src/Utf.cpp.
  • Regression suite covering bounds, truncation, overflow, and corruption (tests/MftRecordParserTests.cpp).
• Sanitizers and fuzzing:
  • CMake options JUSTGIVEMYDISK_ENABLE_SANITIZERS and JUSTGIVEMYDISK_BUILD_FUZZER (disabled by default in normal builds).
  • GitHub Actions CI workflow running CTest under ASan + UBSan and bounded libFuzzer smoke execution (.github/workflows/ntfs-parser-hardening.yml).
  • Target MftRecordParserFuzz exercising raw byte input and mutated structured record skeletons (tests/fuzz/MftRecordParserFuzz.cpp).