d7a17540f8
Added `.clang-tidy` config as discussed in [RFC](https://discourse.llvm.org/t/rfc-create-hardened-clang-tidy-config-for-clang-tidy-directory/87247). Added `bugprone`, `readability`, `modernize`, `performance` checks that didn't create many warnings. Fixed minor warnings to make `/clang-tidy` directory complaint with `clang-tidy-20`. Disabled checks will be enabled in future PRs after fixing their warnings.