Implement Redis-Style Transactions (MULTI/EXEC/DISCARD)

[varunrmantri23]

Changes

This PR introduces Redis-style transaction support to CrimsonCache, allowing clients to execute a sequence of commands atomically.

New Features

• Transaction State: Client structures now track whether they are inside a MULTI block.
• Command Queuing: Commands issued after MULTI are queued rather than immediately executed.
• Atomic Execution: The EXEC command executes all queued commands in order as a single, uninterrupted operation.
• Transaction Abort: The DISCARD command clears the queue and exits the transaction state without executing any commands.
• Error Handling: If an error occurs while queuing commands (e.g., syntax error, out of memory), EXEC will abort the transaction.

New Commands

• MULTI: Starts a transaction block. Subsequent commands are queued.
• EXEC: Executes all commands queued since MULTI.
• DISCARD: Flushes all commands queued since MULTI and exits the transaction state.

Implementation Details

• Created transaction.h and transaction.c to manage transaction logic.
• Modified execute_command in commands.c to check for transaction state and queue commands accordingly.
• Ensured that the original, full command strings (including arguments) are queued and later executed.
• Implemented proper cleanup of transaction state and queued commands after EXEC or DISCARD.

Testing

• Manually tested MULTI/EXEC with various command sequences (SET, GET, INCR).
• Verified that commands are queued and executed in the correct order.
• Confirmed that DISCARD correctly aborts transactions.
• Checked that the server returns to normal command processing after EXEC or DISCARD.
• Ensured that errors during the MULTI phase cause EXEC to abort.