fix: fp16 GPU training

[chebbyChefNEQ]

• cast ivf centroids to the same type as vectors before inference
• cast codebook to the same type as ivf centroid before passing to rust
• fix typing syntax

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.05%. Comparing base (8155c25) to head (f1b6048).

Files with missing lines	Patch %	Lines
rust/lance-index/src/vector/ivf/shuffler.rs	0.00%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3105 +/- ## ========================================== + Coverage 77.03% 77.05% +0.02% ========================================== Files 240 240 Lines 80410 80412 +2 Branches 80410 80412 +2 ========================================== + Hits 61943 61965 +22 + Misses 15265 15263 -2 + Partials 3202 3184 -18 ``` | [Flag](https://app.codecov.io/gh/lancedb/lance/pull/3105/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lancedb) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/lancedb/lance/pull/3105/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lancedb) | `77.05% <0.00%> (+0.02%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=lancedb#carryforward-flags-in-the-pull-request-comment) to find out more.

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[eddyxu]

LGTM