consensus/bor: eliminate contract calls for current span

[manav2401]

Description

This PR replaces the logic to check and commit new spans.

Currently, in every sprint start, we make a contract call to fetch the current span. We check against that span if we need to commit a new one and if yes, we commit it to the contract.

We can easily avoid the contract calls every sprint and make the check very simple and intuitive. Because the span length hasn't changed since genesis, we can simply use a formula to find out which span we're currently in and whether we need to commit a new one.

Changes

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Changes only for a subset of nodes

Breaking changes

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Nodes audience

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Checklist

• I have added at least 2 reviewer or the whole pos-v1 team
• I have added sufficient documentation in code
• I will be resolving comments - if any - by pushing each fix in a separate commit and linking the commit hash in the comment reply
• Created a task in Jira and informed the team for implementation in Erigon client (if applicable)
• Includes RPC methods changes, and the Notion documentation has been updated

Cross repository changes

• This PR requires changes to heimdall
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• This PR requires changes to matic-cli
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Testing

• I have added unit tests
• I have added tests to CI
• I have tested this code manually on local environment
• I have tested this code manually on remote devnet using express-cli
• I have tested this code manually on mumbai/amoy
• I have created new e2e tests into express-cli

Manual tests

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Additional comments

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[manav2401]

fyi, this change makes sure that GetCurrentSpan isn't called even once and the tests still works suggesting that the new implementation is replacable.

[manav2401]

I tried adding a new e2e tests but given default configs, it'll mine ~6400 blocks which will take more time (>1m) and fails under certain cases (which needs more debugging). I believe existing tests should cover most of the cases but if there's a need for a new test and the time is manageable, I don't mind adding it.

Moreover, I can make the time short but we'll have to expose public functions from bor to override the span length and 0th span end as tests assume a smaller test size (this is also something @lucca30 commented above).