fix txn replay for fuzzy region

[vazois]

This PR fixes couple of issues:

1. Our existing transaction replay mechanism keeps track of the operations of a given transaction in a dictionary indexed by sessionID. When a replica encounters a checkpoint marker, it will start buffering the transaction commit markers so it can replay them after encountering the CheckpointEnd marker.
   In that situation, our current solution might intermingle operations between two different transactions from the same session.
2. When replaying the individual operations of a transaction at the replica, there is no locking. In that case, the results of the operations become immediately visible which not desirable given that a reader might see partial results.

In this PR, I am adding the following classes:

• TransactionGroup
  Keeps track of the list of transaction operations
• AofReplayContext
  Keeps track of the replay context and associated objects/buffers used to replay individual operations and transactions.
• AofReplayCoordinator
  Implements the mechanism to keep track of active transactions, gather transaction operations and coordinate transaction replay.

[Copilot]

Pull Request Overview

This PR fixes transaction replay issues during fuzzy region processing in the AOF (Append-Only File) recovery mechanism. The main problem addressed is that the previous implementation could intermingle operations from different transactions with the same session ID, and lacked proper locking during replay which could expose partial transaction results to readers.

Key changes:

• Introduced three new classes (TransactionGroup, AofReplayContext, AofReplayCoordinator) to properly track and coordinate transaction replay operations
• Refactored AOF recovery logic to use the new coordinator pattern with proper transaction isolation
• Updated test infrastructure to support testing both main store and object store replication scenarios

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 22 comments.

Show a summary per file

File	Description
libs/server/AOF/ReplayCoordinator/TransactionGroup.cs	New class to track operations for individual transactions
libs/server/AOF/ReplayCoordinator/AofReplayContext.cs	New class to maintain replay state including fuzzy region buffers and active transactions
libs/server/AOF/ReplayCoordinator/AofReplayCoordinator.cs	New coordinator class implementing transaction tracking, buffering, and replay logic with proper locking
libs/server/AOF/AofProcessor.cs	Refactored to use the new coordinator pattern; simplified recovery logic and removed inline transaction handling
test/Garnet.test.cluster/ClusterTestContext.cs	Added helper methods SimplePopulateDB and SimpleValidateDB to streamline test database operations
test/Garnet.test.cluster/ReplicationTests/ClusterReplicationBaseTests.cs	Updated tests to use new helper methods and support both object store and main store validation

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