feat(rpc): support safe/finalized block tags

[panos-xyz]

Background

Morph Geth PR #278 introduced block tag support (safe / finalized) and related state handling.
Morph-Reth should align with this behavior for RPC compatibility and consistent L2 semantics.

Functional Description

Implement block tag support in Morph-Reth:

• resolve safe / finalized tags in RPC block selection paths
• support updating safe/finalized tags from engine-side input
• keep behavior stable across restart (finalized state persistence if needed)

Scope

• Add safe / finalized block tag resolution in relevant RPC paths
• Add/set safe/finalized block state update entrypoint
• Add persistence/recovery for finalized tag state
• Update related tests and docs

Acceptance Criteria

• safe and finalized tags resolve correctly in RPC endpoints
• tag update path works and is visible through RPC reads
• restart does not lose finalized tag state
• cargo check --workspace passes
• related tests pass

Reference

• Geth PR: Feature: block tag go-ethereum#278
• Design/Discussion: