The metadata subscription handler (updateBucketConfigCacheFromEntry) was
making a separate RPC call via loadCORSFromBucketContent to load CORS
configuration. This created a race window where a slow CreateBucket
subscription event could re-cache stale data after PutBucketCors had
already cleared the cache, causing subsequent GetBucketCors to return
404 NoSuchCORSConfiguration.
Parse CORS directly from the subscription entry's Content field instead
of making a separate RPC. Also fix getBucketConfig to parse CORS from
the already-fetched entry, eliminating a redundant RPC call.
Fix TestCORSCaching to use require.NoError to prevent nil pointer
dereference panics when GetBucketCors fails.
e5f72077ee