Describe the changes

Transactions are now passed alongside blocks to Block Discovery to block validatoin pipeline instead of being fetched during block discovery and then re-fetched in block val.

1. Block Discovery

• handle_block() now accepts pre-fetched BlockTransactions (contains all txs for a block)
• No longer fetches transactions from mempool during discovery
• the get commitment/data txs helpers that are used across the codebase now use mempool read guard instead of mpsc channels.
• we propagate block transactions from block discovery -> block tree -> block validatoin
  this way we don't need to keep re-fetching them from the mempool

2. Block producer

• Returns BlockTransactions alongside block header when producing blocks, useful for tests

3. Block pool

• process_block() now takes BlockTransactions parameter
• Removed reprocess_block() becuase it was no longer used - chian_sync now uses the same process_block

4. Gossip data handler

• New fetch_and_build_block_transactions() - unified tx fetching from cache -> mempool -> DB -> network to build the BlockTransactoins struct
• New fetch_missing_txs_from_network() with peer fallback logic (previously was in-lined code, now its a helper fn)
• Batch queries instead of per-tx checks

Checklist

• Tests have been added/updated for the changes.
• Documentation has been updated for the changes (if applicable).
• The code follows Rust's style guidelines.