Revert "BREAKING: Make random_mod platform-independent"

[tarcieri]

This reverts commit 62b90b8 (#1010)

We're noticing CI failures on cross which seem to be related to this
change, e.g.

https://github.com/RustCrypto/crypto-bigint/actions/runs/19647957432/job/56267760132

It looks like it's potentially getting stuck in an infinite loop.

cc @mrdomino @fjarri

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.86%. Comparing base (2a9c263) to head (4d9ee88).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/uint/rand.rs	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1017      +/-   ##
==========================================
- Coverage   79.88%   79.86%   -0.02%     
==========================================
  Files         163      163              
  Lines       17711    17709       -2     
==========================================
- Hits        14148    14144       -4     
- Misses       3563     3565       +2     

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[mrdomino]

LGTM

Weird!

[tarcieri]

Yeah not sure exactly what's happening

[fjarri]

I guess without that removed masking code in random_mod_core() the rejection takes too long on 32-bit platforms.

[mrdomino]

Not sure that’s it; the i686 tests were passing, and in a different repo I confirmed that that algorithm worked against wasm32.

When I get a chance I’ll give a go at trying to reproduce the cross environment and see if I can figure out what’s going on. Anyone else who’d like to take a swing at it, be my guest.

[tarcieri]

Notably the cross test that was seemingly wedged was actually on aarch64-unknown-linux-gnu, so a 64-bit target, but I have no idea why a problem would arise there but not locally on my M1/M2 Macs