feat: introduce operator fee for OP stack networks

[pedronfigueiredo]

Explanation

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

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Note

Adds OP Stack operator fee to layer1GasFee by querying the oracle (getOperatorFee) and summing with getL1Fee, plus BN utilities and tests.

• Layer 1 Gas Fee (oracle flow):
  • Sum oracle getL1Fee with operator fee from getOperatorFee(gasUsed); default operator fee to zero on failure/undefined; output normalized hex via add0x + padHexToEvenLength.
  • Refactor to BN-based math and value coercion via new toBN; extract #getGasPriceOracleContract; keep default OP Stack oracle address and optional signing.
  • Extend ABI with getOperatorFee.
• Utils:
  • Add bnFromHex and toBN helpers for parsing/converting to BN.
• Tests:
  • Update OracleLayer1GasFeeFlow.test.ts to mock BN returns and cover operator fee present/failure/undefined paths.
  • Add tests for bnFromHex and toBN.
• Docs:
  • Update CHANGELOG.md to note inclusion of operator fee in layer1GasFee.

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