Value Data in separate Segment & Value Data actively persisted features

[grecinto]

Both features mentioned above were seen operational in unit & integration tests. And a lot faster/optimal now.

• When conflict is detected and can be retried for refetch & merge, saved data in separate segment is kept as is and merged as is.

This improvement reduced I/O by a lot by preventing unnecessary delete and re-insert.

[codecov[bot]]

Codecov Report

Attention: 26 lines in your changes are missing coverage. Please review.

Comparison is base (827f325) 71.58% compared to head (1982265) 70.69%. Report is 4 commits behind head on master.

:exclamation: Current head 1982265 differs from pull request most recent head 37ed54e. Consider uploading reports for the commit 37ed54e to get more accurate results

Files	Patch %	Lines
btree/btree.go	43.90%	18 Missing and 5 partials :warning:
btree/store_info.go	0.00%	2 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #24 +/- ## ========================================== - Coverage 71.58% 70.69% -0.89% ========================================== Files 5 5 Lines 1485 1529 +44 ========================================== + Hits 1063 1081 +18 - Misses 302 322 +20 - Partials 120 126 +6 ```

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[grecinto]

The Code coverage report is misleading, as the existing Unit & Integration tests are exercising indirectly even the new code that codecov did not catch.