Catch TimeoutError from runrms

Opening an RMS project can take some time and could timeout after 5 or 10 minutes. This error is not caught by the API, and it should be so a proper error message is shown instead of long error tracebacks. The GUI can then decide to retry opening RMS with different version if it timed out. The TimeoutError should be mapped to HTTP 504 status code.
https://github.com/equinor/fmu-settings-api/blob/6c456d6d13f9d43a4764e9770bcf79a27b256533/src/fmu_settings_api/v1/routes/rms.py#L238-L280

Start in src/fmu_settings_api/v1/routes/rms.py around lines 238-280, where opening an RMS project is handled. Trace how TimeoutError currently propagates and how other errors become API responses. Done means a timeout returns a proper HTTP 504 response that the GUI can use for retry decisions instead of an unhandled traceback.

Written by the indexing model from the issue text.