Bound blob base fee by execution cost (EIP-7918)

[mw2000]

Summary

Floor the blob base fee at the equivalent execution-gas cost so the fee can't drop below an economically meaningful level. Activates with Fusaka.

Spec

• EIP-7918: Blob base fee bounded by execution cost — https://eips.ethereum.org/EIPS/eip-7918

Scope

• Add Fusaka hardfork + EIP-7918 flag to EEVM.HardforkConfig.
• Update the blob base-fee derivation (currently a stub returning 1 wei post-Cancun) to apply the EIP-7918 floor when the flag is active.
• Plumb the new value through EEVM.Context.Block.blob_base_fee.

Definition of Done

• Blob-fee math matches the spec under both Cancun (no floor) and Fusaka (with floor).
• Fusaka blob-tx StateTest fixtures pass.

Parent

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