Replace eager Regex compilation in GitleaksEngine::build() with
OnceLock-based lazy compilation. Individual regexes (rule patterns,
allowlist patterns, global allowlist patterns) are now compiled on
first use rather than at startup. This drops dry-run time from ~1.4s
to ~0.5s since the common no-match path never compiles any regexes.
Also removes the warm_up() pre-loading function and its callers since
lazy compilation makes it unnecessary.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>