*: add lru cache to speed up scanning logs

[BusyJay]

# Master:
test engine::tests::bench_engine_fetch_entries              ... bench:      23,738 ns/iter (+/- 1,027)

# This PR:
test engine::tests::bench_engine_fetch_entries              ... bench:      18,127 ns/iter (+/- 517)

It's not a fair comparison because thread local cache can only cache a block, but global lru cache can cache 256MiB. But it's just a way to show potential improvement on scanning logs.

[codecov]

Codecov Report

Attention: Patch coverage is 94.21769% with 17 lines in your changes missing coverage. Please review.

Project coverage is 97.82%. Comparing base (39f4db4) to head (02f4c85).
Report is 36 commits behind head on master.

Files with missing lines	Patch %	Lines
src/cache.rs	93.51%	14 Missing ⚠️
src/engine.rs	95.08%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #302      +/-   ##
==========================================
- Coverage   97.89%   97.82%   -0.07%     
==========================================
  Files          31       32       +1     
  Lines       12228    12435     +207     
==========================================
+ Hits        11970    12164     +194     
- Misses        258      271      +13     

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[ti-chi-bot]

@BusyJay: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
rust-nightly	02f4c85	link	true	/test rust-nightly

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