feat: read data from write cache

[QuenKar]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

part of #2965

changes:

• move fetch ranges function to helper.rs.
• add read_ranges function for FileCache.
• support to try reading from write cache first, if failed, read from remote object store directly.
• tiny refactor usize to u64

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

#2965

[codecov]

Codecov Report

Attention: 48 lines in your changes are missing coverage. Please review.

Comparison is base (29a7f30) 85.48% compared to head (0d2c646) 85.07%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3128      +/-   ##
==========================================
- Coverage   85.48%   85.07%   -0.42%     
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  Files         822      822              
  Lines      134403   134634     +231     
==========================================
- Hits       114899   114540     -359     
- Misses      19504    20094     +590     

[zhongzc]

most LGTM

[killme2008]

After we merge this PR, could we remove the cache layer?

[QuenKar]

After we merge this PR, could we remove the cache layer?

couldn't be removed yet, because we doesn't implement cache read file now, if data is not in WriteCache and we still rely on cache layer to cache read data. The Write Cache just caches the write file and upload to remote store.

[killme2008]

After we merge this PR, could we remove the cache layer?

couldn't be removed yet, because we doesn't implement cache read file now, if data is not in WriteCache and we still rely on cache layer to cache read data. The Write Cache just caches the write file and upload to remote store.

Got it. I believe our final goal is to merge these two components.

[evenyag]

LGTM.

Could we add a case to test the engine with write cache enabled under mito2::engine mod? It could be done in the next PR.