Replace size_t with uint64_t

[jtraglia]

Opening as a draft. Not entirely sure I want this. I've had some mild concerns with size_t being a dynamic size. I'm not sure if my concerns are justified. This PR replaces all instances of size_t with uint64_t.

[asn-d6]

Can you elaborate on what you think is the issue here? It would be weird if we were accepting size_t as input on a public method, since there could be cross-platform disagreements, but I don't see anything wrong with using the type in internal functions.

[jtraglia]

Hmm I don't have a strong opinion on what internal types we should use. I thought it might be good to use uint64_t everywhere for consistency, but that's not a great reason. Maybe I should revert that, and only do uint64_t for the public API functions, like you suggested. This is originally what I had in mind, but I'm on the fence as to what I think is best.

Screenshot of the task list:

[jtraglia]

I will make these changes sometime next week. Doesn't feel like a high priority right now.

[asn-d6]

This looks good! Thanks!

As a question, is it possible to replace the ulong of the C# bindings to uint64 as well?

c-kzg-4844/bindings/csharp/Ckzg.Bindings/Ckzg.Bindings.cs

Lines 67 to 68 in b58cd9d

	private static extern unsafe KzgResult RecoverCellsAndKzgProofs(byte* recovered_cells, byte* recovered_proofs,
	ulong* cell_indices, byte* cells, ulong num_cells, IntPtr ts);