feat: enforce minimum gas fee floor when Anzeon is enabled

[code0xff]

Summary

When Anzeon is enabled and the chain is past the London fork, this PR enforces a minimum gas fee floor (minBaseFee + gasTip) during txpool validation.
The same rule applies not only to DynamicFeeTx but also to Legacy and AccessList transactions, by using GasFeeCap() (which equals gasPrice for legacy-style txs).

Changes

• Strengthen txpool validation
  • If IsLondon(head.Number) && AnzeonEnabled()
  • Compute minFee = MinBaseFee + GasTip
  • Reject with ErrUnderpriced when tx.GasFeeCap() < minFee
• Add tests
  • Add TestMinimumGasFeeValidation
  • Cover both legacy tx and dynamic fee tx:
    • Below minimum → reject (ErrUnderpriced)
    • At or above minimum → accept
• Adjust existing tests
  • Update some test gas fee values to satisfy the new validation rule

Why

• Under the Anzeon network policy with a base fee floor, prevent transactions below the minimum gas fee from entering the txpool in advance, which:
  • Reduces txpool pollution and spam
  • Ensures consistent enforcement of fee policy

Testing

• Added and passing minimum gas fee validation tests in
  core/txpool/legacypool/legacypool_test.go

Notes

• For LegacyTx and AccessListTx, GasFeeCap() returns gasPrice, so this validation effectively means:
  legacy gasPrice >= MinBaseFee + GasTip

[hominlee-wemade]

LGTM

[0xmhha]

LGTM