Add missing test coverage for Dalli::Server

[mattwd7]

Summary

Substantially expands test coverage for Dalli::Server:

• Initialization: default options, custom option merging, initial state
• Name/hostname parsing: TCP (host, host:port, host:port:weight), UNIX sockets, IPv4, IPv6, FQDN, invalid inputs
• Serializer/compressor accessors: defaults and custom overrides
• close: no-op when nil, socket teardown and state reset
• alive?: sock-present, down_retry_delay period, reconnect after delay
• multi_response_completed? / multi_response_abort: buffer state management
• Request error handling: Timeout::Error closes socket, MarshalError returns false
• serialize: Marshal flags, raw mode, compression thresholds (min/max/per-request), combined flags, MarshalError wrapping
• deserialize: raw, compressed, combined flags, UnmarshalError for bad data, custom serializer error handling
• verify_state: inprogress check, fork detection
• failure! / down! / up!: failure counting, server down lifecycle
• multi?: thread-local state
• split: 64-bit integer splitting
• need_auth? / username / password: option and env variable resolution
• TTL translation: under/over 30-day threshold, timestamp passthrough
• guard_max_value: under-max yield, over-max warning, error mode

Made with Cursor

[mattwd7]

Reviewed 👍