Thread project_alias alongside project_id through the metadata pipeline so
callbacks receive the human-readable project name. DRY up duplicate metadata
dict construction in proxy_track_cost_callback and pass_through_endpoints by
reusing get_sanitized_user_information_from_key — future metadata fields only
need adding in one place.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Krrish Dholakia