Add function to reindex indexes created externally

[var77]

• Add lantern_reindex_external_index function which will get the function pointer from lantern_extras _lantern_reindex_external_index function and call it passing the index params got from index header
• Corresponding PR in lantern_extras https://github.com/lanterndata/lantern_extras/pull/49
• Add new tests for lantern_extras function, we will install lantern extras in Linux platforms and run the tests if extension is installed. It will test the external index creation and reindexing
• Throw error on BuildIndex if index file does not exists and say to use lantern_reindex_external_index function #247

[github-actions[bot]]

Benchmarks

metric	old	new	pct change
recall (after create)	0.740	0.740	-
recall (after insert)	0.724	0.772	+6.63%
select bulk tps	499.890	491.523	-1.67%
select bulk latency (ms)	15.620	15.702	+0.52%
select bulk latency (stddev ms)	2.504	1.967	-21.45%
create latency (ms)	1185.705	1195.361	+0.81%
insert bulk tps	11.293	11.085	-1.84%
insert bulk latency (ms)	88.543	90.200	+1.87%
insert bulk latency (stddev ms)	3.396	2.615	-23.00%
disk usage (bytes)	6348800.000	6348800.000	-

[codecov[bot]]

Codecov Report

Merging #250 (4c1583b) into main (c129d8a) will decrease coverage by 0.41%. The diff coverage is 70.68%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #250 +/- ## ========================================== - Coverage 82.18% 81.77% -0.41% ========================================== Files 17 17 Lines 1375 1432 +57 Branches 311 319 +8 ========================================== + Hits 1130 1171 +41 - Misses 108 119 +11 - Partials 137 142 +5 ``` | [Files](https://app.codecov.io/gh/lanterndata/lantern/pull/250?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lanterndata) | Coverage Δ | | |---|---|---| | [src/hnsw.c](https://app.codecov.io/gh/lanterndata/lantern/pull/250?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lanterndata#diff-c3JjL2huc3cuYw==) | `80.36% <100.00%> (+0.45%)` | :arrow_up: | | [src/hnsw/build.c](https://app.codecov.io/gh/lanterndata/lantern/pull/250?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lanterndata#diff-c3JjL2huc3cvYnVpbGQuYw==) | `78.29% <67.92%> (-2.58%)` | :arrow_down: |