Fix event sequence

[bukk530]

Key Changes

Checkpoint Handling Fixes:

• Fixed FileCheckpointStore and MongoCheckpointStore to enforce monotonic checkpoint advancement - checkpoints can no longer move backwards within a run
• Modified Replicator.Flush() to rely on the checkpoint store's in-memory state rather than computing a checkpoint from the reader's position
• Added ReplicationRun helper to generate a unique RunId per replication execution for log correlation

Partition Sequencing Improvements:

• Changed PartitionChannel to use global commit position (SourceLogPosition.EventPosition) for ordering instead of per-stream SequenceNumber, fixing false sequence errors when new streams start at event number 0
• Added IsMetadata computed property to BaseOriginalEvent and BaseProposedEvent to distinguish metadata/system events ($>, $@) from domain events
• Added IgnoreMetadataEventsForPartitioning configuration flag to optionally bypass sequence checks for metadata events

Diagnostic Instrumentation:

• Added ReplicationMessageId (GUID) to all event models for end-to-end correlation from reader → partitioner → Kafka writer
• Added DebugPartitionSequences configuration flag to enable high-verbosity sequencing logs
• Enhanced PartitionChannel with detailed logging:
  • Sequence transitions with delta values
  • Buffer dumps on sequence errors (last 32 events)
  • Last successfully written event before errors
  • Per-event Seq OK logs when debug mode is enabled
• Enhanced checkpoint logging with RunId, source (InMemory/File/Default), and previous/new values on flush
• Added event classification logging in GrpcEventReader and TcpEventReader

Configuration:

• Added Replicator.DebugPartitionSequences setting for enabling verbose diagnostic logs
• Added Sink.IgnoreMetadataEventsForPartitioning setting for metadata handling control
• Both settings are propagated through SinkPipeOptions and logged at startup when enabled

Files Modified

• src/Kurrent.Replicator/Replicator.cs
• src/Kurrent.Replicator/FileCheckpointStore.cs
• src/Kurrent.Replicator/Partitioning/PartitionChannel.cs
• src/Kurrent.Replicator/Partitioning/HashPartitioner.cs
• src/Kurrent.Replicator/Partitioning/ValuePartitioner.cs
• src/Kurrent.Replicator/Sink/SinkPipe.cs
• src/Kurrent.Replicator/Sink/SinkPipelineOptions.cs
• src/Kurrent.Replicator.Shared/Contracts/OriginalEvent.cs
• src/Kurrent.Replicator.Shared/Contracts/ProposedEvent.cs
• src/Kurrent.Replicator.Shared/Observe/ReplicationRun.cs (new)
• src/Kurrent.Replicator.Shared/Observe/ReplicationDebugOptions.cs (new)
• src/Kurrent.Replicator.KurrentDb/GrpcEventReader.cs
• src/Kurrent.Replicator.EventStore/TcpEventReader.cs
• src/Kurrent.Replicator.Kafka/KafkaWriter.cs
• src/Kurrent.Replicator.Mongo/MongoCheckpointStore.cs
• src/replicator/Settings/ReplicatorSettings.cs
• src/replicator/Startup.cs

Testing

• All existing tests pass
• Kafka writer tests (10 tests) verified working correctly
• Manual testing confirmed checkpoint advances correctly and sequence errors are properly detected