Fix partial writes

[salman01zp]

Summary of changes

• Fix partial write issue with computing Merkle root in can_handle_evensts, moved it to handle_events
• Group operation for LeafStoreCache traits using sled atomic transactions https://docs.rs/sled/latest/sled/transaction/index.html

store.insert_leaves()
// This is the last deposit event block number
store.insert_last_deposit_block_number()
// This will be used by the event watcher to track the block number that has been processed
store.set_last_block_number()

Reference issue to close (if applicable)

• Closes #506

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Code Checklist

• [x] Tested
• [ ] Documented