Ghostferry GTID checkpointing and source failover recovery

[driv3r]

GTID checkpointing:

• GTID 1/5: Introduce BinlogCoordinate abstraction (file/position backed) #445
• GTID 2/5: Add coordinate mode (representation + config + reads) #446
• GTID 3/5: Binlog streaming start/stop (behind mode flag) #447
• GTID 4/5: Persist GTID coordinates in state, enable resume, test both modes in CI #448
• GTID 5/5: GTID-aware replica catchup #449

Source Failover Recovery:

• Introduce SourceRuntime to own the source connection (GTID failover 1/3) #451
• Migrate source consumers to SourceRuntime (GTID failover 2/3) #452
• GTID master failover recovery + integration test (GTID failover 3/3) #453