Integrate UploadHandler in BufferedWriteHandler struct

[ashmeenkaur]

Description

This PR integrates the UploadHandler into the BufferedWriteHandler to enable efficient and synchronized uploads of filled blocks to GCS.

Key changes

• Trigger block uploads: When a block in the BufferedWriteHandler is complete, it's automatically sent to the UploadHandler for asynchronous uploading.
• Implement Flush method: A Flush method is added to BufferedWriteHandler. This method ensures current block is sent for upload and then calls the Finalize method on the UploadHandler to finalize the GCS object.

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - Manually verified the happy path upload of a file with buffered writes enabled.
2. Unit tests - updated
3. Integration tests - NA

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 77.58%. Comparing base (039429f) to head (fa29ea7).

Files with missing lines	Patch %	Lines
internal/bufferedwrites/buffered_write_handler.go	78.57%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@                Coverage Diff                @@
##           uploadHandler    #2670      +/-   ##
=================================================
+ Coverage          77.55%   77.58%   +0.02%     
=================================================
  Files                112      112              
  Lines              15797    15803       +6     
=================================================
+ Hits               12252    12261       +9     
+ Misses              3022     3019       -3     
  Partials             523      523              

Flag	Coverage Δ
unittests	77.58% <80.00%> (+0.02%)	⬆️

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