Remove the redundant ErrorCoder type assertion and let the
recursive call handle unsupported error types.
Make all switch cases return explicitly.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Add missing mappings for ErrFailedPrecondition (412) and
ErrResourceExhausted (429), aligning with containerd's errhttp
implementation.
Add table-driven tests covering the errdefs mappings, gRPC and
distribution errors, and wrapped and joined errors.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>