meta: optimizate the rmr emptyDir

[Xuyuchao-juice]

How about this PR
New low-level doEmptyDir interface, to batch delete files, can optimize metadata operations.

Test Reslut:
Delete a directory with 10,000 empty files

[codecov]

Codecov Report

❌ Patch coverage is 8.25688% with 200 lines in your changes missing coverage. Please review.
✅ Project coverage is 22.11%. Comparing base (c4cfbee) to head (6677229).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/meta/sql.go	0.00%	181 Missing ⚠️
pkg/meta/utils.go	48.38%	13 Missing and 3 partials ⚠️
pkg/meta/redis.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6457      +/-   ##
==========================================
- Coverage   22.29%   22.11%   -0.18%     
==========================================
  Files          30       30              
  Lines       20446    20688     +242     
==========================================
+ Hits         4558     4575      +17     
- Misses      15377    15601     +224     
- Partials      511      512       +1     

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