Implement transaction gas limit cap (EIP-7825)

[mw2000]

Summary

Cap any single transaction's gas_limit at 2^24 = 16,777,216. Activates with Fusaka.

Spec

• EIP-7825: Transaction Gas Limit Cap — https://eips.ethereum.org/EIPS/eip-7825

Scope

• Add Fusaka (:osaka / :fusaka) to EEVM.HardforkConfig with EIP activation flag.
• Reject any transaction with gas_limit > 16_777_216 in EEVM.Transaction.Validator when the flag is enabled.

Definition of Done

• Fixtures under BlockchainTests/.../EIP7825* pass via the test harness.
• Negative-path test: oversized gas_limit produces a validation error.

Parent

• EVM Completeness: Missing opcodes, precompiles, and gas rules #30 — EVM Completeness tracking issue