regex perf improvements

[ZhidongPeng]

• Regex::New is performance-sensitive - use LazyLock to compile it only once as a static regex and reuse it for subsequent calls
• search_files should not create a new regex instance each time, and the caller should cache the regex if it is used frequently.
• Config setting value get_xxx in Config invoked resolve_env_variables at each call - resolve all the config values at new when first read & parse our config file.
• regex.replace_all's time-complexity is O(m * n^2) in redact_secrets - first check for indicators, just simple substrings to check for before running the more expensive regexes.