refactor: engine refactor

[bsbds]

Depends-On: #703

Implements StorageOps for Engine

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

[mergify[bot]]

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.90476% with 66 lines in your changes missing coverage. Please review.

Project coverage is 75.87%. Comparing base (e35b35a) to head (9bc7c64). Report is 135 commits behind head on master.

Files	Patch %	Lines
crates/engine/src/rocksdb_engine/transaction.rs	83.70%	14 Missing and 8 partials :warning:
crates/engine/src/proxy.rs	90.71%	17 Missing :warning:
crates/engine/src/rocksdb_engine/mod.rs	90.47%	3 Missing and 5 partials :warning:
crates/engine/src/memory_engine/mod.rs	88.70%	5 Missing and 2 partials :warning:
crates/curp/src/server/storage/db.rs	0.00%	0 Missing and 5 partials :warning:
crates/engine/src/memory_engine/transaction.rs	0.00%	4 Missing :warning:
crates/xline/src/storage/db.rs	60.00%	1 Missing and 1 partial :warning:
crates/engine/src/api/operation.rs	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #673 +/- ## ========================================== + Coverage 75.55% 75.87% +0.32% ========================================== Files 180 186 +6 Lines 26938 28024 +1086 Branches 26938 28024 +1086 ========================================== + Hits 20353 21264 +911 - Misses 5366 5450 +84 - Partials 1219 1310 +91 ```

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