Mempool: improve selection algorithm

[andreibancioiu]

Reasoning behind the pull request

• Transactions selection (from mempool) is sub-optimal: sorting is sub-optimal, while the volume of selected transactions isn't wisely measured / capped (and, in conjunction with the front-running protection, this sometimes produces undesirable effects - blocks not being full).
• Scheduled processing interacts with the transactions selection & nonce notification, and leads to sub-optimal processing of transactions (and blocks not being full).

Proposed changes

1. Integrate the changes from Improve selection algorithm mx-chain-storage-go#55 - transactions are selected with respect to their price per gas unit.
2. When selecting transactions, use an upper bound of the accumulated gas.
3. Feed an account nonce provider (backed by an accounts adapter) to shardedTxPool - see (4).
4. When adding a transaction to the mempool, inform it about the current nonce of the sender.
5. Upon regular or scheduled processing, notify the mempool, inform it about current account nonces.
6. When reverting a block, ask the mempool to forget about all known nonces. This is slightly suboptimal (but should be fine in practice) - we should have asked the mempool to do a selective forget (only for the senders that participated in the reverted block) - left as future work.

Testing procedure

• Standard testing
• Heavy load, to trigger evictions from the mempool
• Trigger reverted blocks

Pre-requisites

Based on the Contributing Guidelines the PR author and the reviewers must check the following requirements are met:

• was the PR targeted to the correct branch?
• if this is a larger feature that probably needs more than one PR, is there a feat branch created?
• if this is a feat branch merging, do all satellite projects have a proper tag inside go.mod?

[github-actions]

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🔄 Build Details:

• mx-chain-go Commit Hash: 3ddc19fa402d74d2457bbb2a093c150e7656f9ed
• Current Branch: selection-by-ppu
• mx-chain-go Target Branch: rc/spica-patch-mempool
• mx-chain-simulator-go Target Branch: selection-by-ppu
• mx-chain-testing-suite Target Branch: main

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• PYTEST_EXIT_CODE: 0
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