eth: handle nil blocks and state when pending is not available

[manav2401]

Description

This PR includes a subset of changes from ethereum/go-ethereum#27218 which checks for nil header, state and receipt values when node is syncing and calls to pending are made.

Note that the rest of the changes in the PR will be pulled in routine upstream merge. Only the required fix is pulled.

This PR also handles nil state or error in the SendRawTransactionConditional api.

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

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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