feat(l1): save header download checkpoint + skip downloading pre-pivot bodies + track pending sync [WIP]

[fmoletta]

Motivation
This PR tackles the following problems:

• Having to download all headers for each sync cycle
• Fork choice update & new payloads being applied on top of non-synced state
  And also temporarily simplifies snap syncing by not downloading bodies and receipts for blocks before the pivot. (WARNING: this goes against the spec but shouldn't be a problem for the time being)

Description

• Stores the last downloaded block's hash in the DB during snap sync to serve as a checkpoint if the sync is aborted halfway (common case when syncing from genesis). This checkpoint is cleared upon succesful snap sync.
• No longer fetches receipts or block bodies past the pivot block during snap sync
• Add method sync_status which returns an enum with the current sync status (either Inactive, Active or Pending) and uses it in the ForkChoiceUpdate & NewPayload engine rpc endpoints so that we don't apply their logic during an active or pending sync.

Closes None

[github-actions]

| File                                                                        | Lines | Diff |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/cmd/ethrex/ethrex.rs                        | 339   | -1   |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/networking/p2p/net.rs                | 884   | -8   |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/networking/p2p/sync.rs               | 604   | +3   |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/networking/rpc/engine/fork_choice.rs | 269   | +4   |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/networking/rpc/engine/payload.rs     | 335   | +10  |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/networking/rpc/rpc.rs                | 450   | +16  |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/engines/api.rs         | 162   | +3   |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/engines/in_memory.rs   | 389   | +16  |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/engines/libmdbx.rs     | 756   | +34  |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/engines/utils.rs       | 46    | +14  |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/storage.rs             | 1161  | +9   |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/vm/levm/src/errors.rs                | 235   | -4   |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/vm/levm/src/gas_cost.rs              | 881   | -50  |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/vm/levm/src/precompiles.rs           | 955   | -245 |
+-----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/vm/vm.rs                             | 766   | -51  |
+-----------------------------------------------------------------------------+-------+------+

Total lines added: +109
Total lines removed: 359
Total lines changed: 468