[Storage] Add Closer to Batch interface and use it to prevent memory leak (BadgerDB & Pebble)

[fxamacker]

Closes #7258
Updates #6527

Currently, the Batch interface doesn't provide a Close function to release memory of the batch. Not calling the database function to close or cancel a batch can cause "unbounded memory consumption" according to BadgerDB v2 docs. And for Pebble, we should use Batch.Close() for both non-error and error paths.

This PR adds a Closer to Batch interface so it can be used to release memory of the batch. The Close() function can be called as a defer statement immediately after creating Batch to reduce risk of unbounded memory consumption.

This PR also updates existing code to call Close() after a new Batch is created.

I found this while getting familiar with storage code related to BadgerDB and Pebble.

Details

BadgerDB v2 docs for WriteBatch.Cancel() says:

Cancel function must be called if there's a chance that Flush might not get called. If neither Flush or Cancel is called, the transaction oracle would never get a chance to clear out the row commit timestamp map, thus causing an unbounded memory consumption. Typically, you can call Cancel as a defer statement right after NewWriteBatch is called.

For example, the error path in WithReaderBatchWriter() currently has a memory leak when using BadgerDB.

Pebble docs says for Batch.Close():

Close closes the batch without committing it.

Pebble needs their Batch.Close() function to be called for both non-error and error paths.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 68.18182% with 14 lines in your changes missing coverage. Please review.

Project coverage is 41.32%. Comparing base (9fa5d10) to head (7ad6c30).

Files with missing lines	Patch %	Lines
storage/mock/batch.go	0.00%	12 Missing ⚠️
...ck-executed-height/cmd/rollback_executed_height.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7257   +/-   ##
=======================================
  Coverage   41.31%   41.32%           
=======================================
  Files        2174     2174           
  Lines      190514   190558   +44     
=======================================
+ Hits        78713    78745   +32     
- Misses     105223   105236   +13     
+ Partials     6578     6577    -1     

Flag	Coverage Δ
unittests	41.32% <68.18%> (+<0.01%)	⬆️

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[zhangchiqing]

Thanks for the fix Faye.

[janezpodhostnik]

Great change!