Handle standard errors in meta protocol parser

[mrattle]

Summary

• parse standard memcached error responses in meta protocol handlers
• map ERROR, CLIENT_ERROR, and SERVER_ERROR to existing ErrorKind variants
• drain the internal quiet-mode no-op response after non-no-op quiet meta responses so pooled/reused clients stay stream-aligned
• report unexpected quiet drain responses by response kind/status
• add parser coverage for meta get/set/delete/arithmetic error responses
• add fake-server quiet-mode regression coverage for meta_get, meta_set, meta_delete, meta_increment, and meta_decrement, including follow-up requests on the same client
• add fake-server coverage for unexpected quiet drain status/data responses

Testing

• cargo fmt
• cargo test 'test_quiet_meta' --test meta_proto_integration_tests
• cargo test