split sanitizers into per-sanitizer features, flags, and constraints

[RSingh1511]

Summary

Split sanitizers into independent, composable units — each sanitizer (ASan, UBSan, LSan, TSan) now has its own bool_flag, Bazel feature, and execution constraint
Enables enabling any single sanitizer in isolation (--config=asan, --config=tsan, etc.)
Supports selective composition (--config=asan_ubsan_lsan)
Adds fine-grained constraints (no_asan, only_tsan, etc.) to skip tests incompatible with a specific sanitizer

Notes for Reviewer

Pre-Review Checklist for the PR Author

• PR title is short, expressive and meaningful
• Commits are properly organized
• Relevant issues are linked in the References section
• Tests are conducted
• Unit tests are added

Checklist for the PR Reviewer

• Commits are properly organized and messages follow S-CORE commit guidelines
• Unit tests have been written for new behavior
• Public API is documented
• PR title describes the changes

Post-review Checklist for the PR Author

• All open points are addressed and tracked via issues

References

Closes #4