fix(core,txpool,ethapi): reject overflowing tx values

[gzliudan]

Proposed changes

Reject transaction values above uint256 max during txpool validation and execution.

Map the overflow to an invalid params RPC error and add focused unit tests.

fix #2287

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• test: Adding missing tests or correcting existing tests

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• Consensus
• Account
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• Geth
• Smart Contract
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Checklist

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• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Tested on a private network from the genesis block and monitored the chain operating correctly for multiple epochs.
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
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[Copilot]

Pull request overview

This PR hardens transaction handling by rejecting transaction value fields that exceed the uint256 maximum during txpool validation and EVM execution, and ensures the overflow is surfaced as an invalid-params style RPC validation error (where txValidationError is used).

Changes:

• Add value overflow checks (BitLen() > 256) in txpool validation and EVM state transition.
• Map ErrUint256Overflow to errCodeInvalidParams in txValidationError.
• Add targeted unit tests covering overflow rejection paths in ethapi, txpool, and state processing.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
internal/ethapi/errors.go	Maps ErrUint256Overflow to an invalid-params tx validation RPC error.
internal/ethapi/api_test.go	Adds ethapi tests for overflow rejection and tx validation error mapping.
core/txpool/validation.go	Rejects transactions whose value exceeds uint256 during basic tx validation.
core/txpool/legacypool/legacypool_test.go	Adds a pool-level unit test asserting overflow values are rejected.
core/state_transition.go	Treats value conversion overflow as ErrUint256Overflow during execution.
core/state_processor_test.go	Adds an execution-level test ensuring ApplyTransactionWithEVM rejects overflow values.

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