Consumer: use new proto attrs in Fetcher (ListOffsets/Fetch)

[dpkp]

• Consumer: use new proto attrs in Fetcher (ListOffsets/Fetch)
• KafkaNetClient: use manager.broker_version property
• kafka.util: raise from None to clean KeyError
• fetcher: prefer _manager to _client
• fix typo
• handle timestamp / leader_epoch None -> defaults
• Drop _client.connected and _client.ready checks in _create_fetch_requests
• Fix to_send / to_forget encoding
• Drop unused NoOffsetForPartitionError
• optional timeout_ms for offset lookups
• revert ListOffsets max_version = 5; add detailed TODO
• docstrings
• partition => tp
• Drop version guard from offsets_for_times (protocol will handle if necessary)