[datastore]: handle insert scenario where bundle hash is the same

[wlawt]

Overview

This PR addresses the API spec for the following scenario:

If a bundle with the same bundle hash already exists the bundle will be combined with the existing one.

The assumptions are that the txs, txn_hashes, reverting_txs all remain the same. Properties that we "combine" would be the following (open to changing any of them):

• Min base fee
• Block number
• Min/max timestamp

The "combining" logic is simply just updating with the incoming bundle, for now. This can be changed later on.

Tests

• Added unit test insert_bundle_with_same_bundle_hash
• Fixed the other unit tests in the file. Specifically, added a generate_tx fn to uniquely generate different txns so that this change wouldn't break all the existing unit tests, as it was testing other functionalities, which I assumed the functionality was assuming bundles would have different hashes.

[wlawt]

wait until new in-memory BundlePool is impl