MRG: standardize on u32 for scaled, and introduce ScaledType

[ctb]

Makes scaled a u32, and change a few others as well.

This PR started because we were mixing u32 and u64 in places, but I think a switch away from usize (architecture specific & mostly returned from collection lengths, and so on) to explicit u32/u64 seems good.

Fixes #3363

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.45%. Comparing base (122c4b7) to head (5f49d1c).
Report is 1 commits behind head on latest.

Files with missing lines	Patch %	Lines
src/core/src/ffi/index/revindex.rs	0.00%	1 Missing ⚠️

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@@            Coverage Diff             @@
##           latest    #3364      +/-   ##
==========================================
- Coverage   86.45%   86.45%   -0.01%     
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  Files         137      137              
  Lines       16090    16089       -1     
  Branches     2219     2219              
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- Hits        13911    13910       -1     
  Misses       1872     1872              
  Partials      307      307              

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python	92.40% <ø> (ø)
rust	62.16% <93.33%> (-0.02%)	⬇️

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[ctb]

Ready for review @luizirber

[luizirber]

This PR started because we were mixing u32 and u64 in places, but I think a switch away from usize (architecture specific & mostly returned from collection lengths, and so on) to explicit u32/u64 seems good.

Initially u32 started to get into the API because wasm is 32-bits nowadays, so some function calls were easier to set up across JS/Rust. But also based on the scaled values we actually use (1 -> ~100k) u64 is way too big, u16 is too small, so... u32 it is?

(ksize should probably be u16, has anyone ever used k > 65535? 😹 )

I would have no problem standardizing scaled on u32, too. Just want it to be one type of number :).

Maybe we can do a type alias like HashIntoType for scaled:

sourmash/src/core/src/lib.rs

Line 55 in 6ae9cd3

type HashIntoType = u64;

would likely still need some conversions but can be done with as HashIntoType.
(And easier to play out with changing the type too and evaluating consequences, instead of having to fix everywhere in the codebase)

[ctb]

sounds good!

[ctb]

Ready for review @luizirber !

[ctb]

k! was wondering where to do the conversion ;)

[luizirber]

ScaledType is just an alias, so it gets resolved to u32 in include/sourmash.h. So it doesn't change much now, but easier to play with different ScaledType values in the future =]