perf(levm): refactor libmdbx storage, removing unneeded rlp encoding

[edg-l]

Motivation

Remove unneeded RLP encoding from key/values in libmdbx / redb storage

The database tables are completly private so we don't need to use rlp encoding at all, avoiding possible perfomance costs by storing as bytes directly where possible.

Complex types like entire blocks remain as RLP, future improvements could be made, like changing to a possibly more perfomant encoding like bincode.

[github-actions]

Lines of code report

Total lines added: 48
Total lines removed: 47
Total lines changed: 95

Detailed view

+-------------------------------------------+-------+------+
| File                                      | Lines | Diff |
+-------------------------------------------+-------+------+
| ethrex/crates/storage/rlp.rs              | 95    | -7   |
+-------------------------------------------+-------+------+
| ethrex/crates/storage/store_db/libmdbx.rs | 1415  | -40  |
+-------------------------------------------+-------+------+
| ethrex/crates/storage/store_db/mod.rs     | 35    | +30  |
+-------------------------------------------+-------+------+
| ethrex/crates/storage/store_db/redb.rs    | 1288  | +18  |
+-------------------------------------------+-------+------+

[github-actions]

Benchmark Block Execution Results Comparison Against Main

Command	Mean [s]	Min [s]	Max [s]	Relative
base	162.668 ± 0.585	161.563	163.504	1.01 ± 0.00
head	160.882 ± 0.528	159.901	161.352	1.00