⚡ Bolt: [performance improvement] Cache workspace credentials read

[mapleleaflatte03]

💡 What: Added @functools.lru_cache(maxsize=1) to _load_workspace_credentials
🎯 Why: _load_workspace_credentials is called frequently (e.g. on every _is_authorized call for Basic Auth routes and in multiple other places) and performs disk I/O os.path.exists and open().read() each time. Caching it prevents unnecessary disk I/O, speeding up requests.
📊 Impact: Significantly reduces file I/O operations and latency on HTTP requests protected by Basic Auth.
🔬 Measurement: Observe reduced latency in processing requests using Basic Auth and fewer file operations via profiling.

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PR created automatically by Jules for task 9087685244821708226 started by @mapleleaflatte03

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