Add -Wconversion

[MarcinKonowalczyk]

Add warnings to prevent implicit conversions. It's a simple change and the library is already compliant.

cmake .. -DCGLM_USE_TEST=ON -DCGLM_SHARED=ON && make && make check passes

Thoughts?

[MarcinKonowalczyk]

So far unrelated CI failures ("Error: retrieving gpg key timed out.")

[recp]

Hi @MarcinKonowalczyk, thanks for your contributions the PR is merged 🚀

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PS: I actually like implicit conversions especially for integers 🫣 but no need to have them in cglm ( for now especially )