Fix int overflow issue for progress

[var77]

As the progress was int32, the progress was overflowing if index is bigger than ~2GB.

[codecov[bot]]

Codecov Report

Merging #186 (545c4ae) into main (29af187) will not change coverage. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #186 +/- ## ======================================= Coverage 83.09% 83.09% ======================================= Files 17 17 Lines 1201 1201 Branches 256 256 ======================================= Hits 998 998 Misses 81 81 Partials 122 122 ``` | [Files](https://app.codecov.io/gh/lanterndata/lantern/pull/186?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lanterndata) | Coverage Δ | | |---|---|---| | [src/hnsw/external\_index.c](https://app.codecov.io/gh/lanterndata/lantern/pull/186?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lanterndata#diff-c3JjL2huc3cvZXh0ZXJuYWxfaW5kZXguYw==) | `91.09% <100.00%> (ø)` | |

[github-actions[bot]]

Benchmarks

metric	old	new	pct change
recall (after create)	0.740	0.740	-
recall (after insert)	0.774	0.758	-2.07%
select bulk tps	221.794	236.280	+6.53%
select bulk latency (ms)	34.222	30.683	-10.34%
select bulk latency (stddev ms)	10.459	13.949	+33.37%
create latency (ms)	1458.342	1565.197	+7.33%
insert bulk tps	13.953	14.122	+1.21%
insert bulk latency (ms)	71.652	70.799	-1.19%
insert bulk latency (stddev ms)	6.077	2.105	-65.36%
disk usage (bytes)	6348800.000	6348800.000	-