refactor: Index

[bsbds]

Please briefly answer these questions:

• what problem are you trying to solve? (or if there's no problem, what's the motivation for this change?)

• what changes does this pull request make?

• are there any non-obvious implications of these changes? (does it break compatibility with previous versions, etc)

[mergify[bot]]

@bsbds Convert your pr to draft since CI failed

[Phoenix500526]

@Mergifyio rebase

[mergify[bot]]

rebase

✅ Branch has been successfully rebased

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 81.89189% with 67 lines in your changes missing coverage. Please review.

Project coverage is 75.70%. Comparing base (e35b35a) to head (3d0329c). Report is 135 commits behind head on master.

:exclamation: Current head 3d0329c differs from pull request most recent head 2f23248

Please upload reports for the commit 2f23248 to get more accurate results.

Files	Patch %	Lines
crates/xline/src/storage/index.rs	82.50%	59 Missing and 4 partials :warning:
crates/xline/src/storage/kv_store.rs	57.14%	0 Missing and 3 partials :warning:
crates/xline/src/server/command.rs	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #807 +/- ## ========================================== + Coverage 75.55% 75.70% +0.14% ========================================== Files 180 188 +8 Lines 26938 28039 +1101 Branches 26938 28039 +1101 ========================================== + Hits 20353 21226 +873 - Misses 5366 5517 +151 - Partials 1219 1296 +77 ```

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[mergify[bot]]

@bsbds Convert your pr to draft since CI failed

[Phoenix500526]

Please squash these commits into one.

[mergify[bot]]

@bsbds Your PR is in conflict and cannot be merged.

[mergify[bot]]

@bsbds Convert your pr to draft since CI failed

[mergify[bot]]

@bsbds Convert your pr to draft since CI failed