Cache warm no longer parses Xcode activity logs

tuist cache warm no longer copies and parses .xcactivitylog files to infer per-target build durations. The unused XCLogParser-based parser is removed, target build duration is dropped from cache storable metadata and command-event binary cache metadata, and cache warm no longer fails when activity logs are missing or unparseable. The existing server/OpenAPI fields are kept for backward compatibility with older clients.