The picker path fetches the Copilot /models catalog multiple times per
process (list_authenticated_providers -> provider_model_ids ->
_fetch_github_models, plus get_copilot_model_context / normalize
helpers). Cache the filtered catalog at module level with a short TTL
so repeated picker opens do not pay a TLS handshake each time.
Fold-fixes on top of the original patch:
- key the cache by api_key so a mid-process credential swap never
serves the previous account's catalog
- use time.monotonic() so wall-clock adjustments cannot extend the TTL
- deep-copy on store/serve so callers cannot mutate cached entries
- tests updated to patch _urlopen_model_catalog_request (main routes
catalog fetches through open_credentialed_url now), plus TTL-expiry
and credential-change coverage
Extracted from #40276.
