feat: impl raft store log enc dec, adjust dir structure

[MrCroxx]

As titled.

Ref: #44

[codecov]

Codecov Report

Merging #84 (7faed7c) into main (55cb955) will increase coverage by 0.18%.
The diff coverage is 96.59%.

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
+ Coverage   87.07%   87.25%   +0.18%     
==========================================
  Files          55       56       +1     
  Lines        4409     4497      +88     
==========================================
+ Hits         3839     3924      +85     
- Misses        570      573       +3     

Impacted Files	Coverage Δ
storage/src/lib.rs	100.00% <ø> (ø)
storage/src/lsm_tree/components/block.rs	95.32% <ø> (ø)
storage/src/lsm_tree/components/memtable.rs	100.00% <ø> (ø)
storage/src/lsm_tree/components/skiplist/arena.rs	100.00% <ø> (ø)
storage/src/lsm_tree/components/skiplist/key.rs	48.38% <ø> (ø)
storage/src/lsm_tree/components/skiplist/list.rs	85.75% <ø> (ø)
storage/src/lsm_tree/components/sstable.rs	86.14% <ø> (ø)
storage/src/lsm_tree/iterator/block_iterator.rs	100.00% <ø> (ø)
storage/src/lsm_tree/iterator/concat_iterator.rs	98.52% <ø> (ø)
storage/src/lsm_tree/iterator/memtable_iterator.rs	100.00% <ø> (ø)
... and 7 more

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