Harden concurrent cache project

[FILWYZ]

What changed

• fix the misspelled LRU namespace and align it with the shared CachePolicy API
• enforce exact capacity across LRU shards and add atomic hit/miss/eviction statistics
• add CMake/CTest coverage for eviction, LRU-K promotion, LFU/ARC behavior, capacity, and concurrent access
• add GCC/Clang GitHub Actions with ASan/UBSan and a benchmark smoke test
• remove generated benchmark sources and binary from version control
• rewrite the README with reproducible build, test, benchmark, architecture, and scope documentation
• add an MIT license

Why

The benchmark on main did not compile because LRU.h used the Cachae
namespace while the rest of the project and benchmark used Cache. The LRU
implementation also lacked the statistics interface described by the README,
and generated build artifacts were committed to the repository.

Impact

The header-only API now compiles consistently, LRU capacity is no longer
inflated when the requested shard count exceeds capacity, and the repository
has a repeatable local and CI validation path.

Validation

• Release CMake build and CTest
• Debug build with AddressSanitizer and UndefinedBehaviorSanitizer
• 4-thread benchmark smoke run: 20,000 operations per scenario, capacity 512, 4 shards
• git diff --check