test: engine with write cache

[QuenKar]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

PLEASE DO NOT LEAVE THIS EMPTY !!!

• add write cache test for engine
• remove unused for file cache and write cache
• refactor my code style, use crate path instead of super

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)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1294d6f) 85.54% compared to head (75ef328) 84.96%.

❗ Current head 75ef328 differs from pull request most recent head 48b5c75. Consider uploading reports for the commit 48b5c75 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3163      +/-   ##
==========================================
- Coverage   85.54%   84.96%   -0.59%     
==========================================
  Files         829      827       -2     
  Lines      135711   135311     -400     
==========================================
- Hits       116096   114962    -1134     
- Misses      19615    20349     +734     

[fengjiachun]

LGTM