fix(l1): don't trigger snap sync if fcu head is already canonical

[fmoletta]

Motivation
In hive tests we often receive an fcu with either the genesis or last imported block as head to notify the node that it is already synced. As this is not usual in a real-case scenario, we just trigger a snap sync to the advertised head. This PR solves this by first checking if the fcu head is already part of our canonic chain before triggering a sync

Description

• When handling a forkchoice in snap sync mode, check that the head is not already canonical before triggering a sync, if it is already canonical, apply the forkchoice

Closes #4846

[github-actions]

Lines of code report

Total lines added: 10
Total lines removed: 0
Total lines changed: 10

Detailed view

+----------------------------------------------------+-------+------+
| File                                               | Lines | Diff |
+----------------------------------------------------+-------+------+
| ethrex/crates/networking/p2p/sync_manager.rs       | 132   | +3   |
+----------------------------------------------------+-------+------+
| ethrex/crates/networking/rpc/engine/fork_choice.rs | 367   | +7   |
+----------------------------------------------------+-------+------+

[mpaulucci]

In that case, will the sync mode be set as Full somewhere?

[fmoletta]

The next FCU to an unknown head will trigger a sync, the syncer will detect that the sync_head is only a few blocks away and switch to full sync mode

[fmoletta]

Update: changed to also disable snap sync so we can process incoming new payloads right away

[mpaulucci]

Please verify that hive --sim ethereum/engine --sim.limit "engine-auth/" passes all tests when on snap sync mode, see https://github.com/ethereum/hive/blob/7709e5892146c793307da072e1593f48039a7e4b/clients/ethrex/ethrex.sh#L79