Update rand and nalgebra with opt-in wasm_js support

[day01]

MOTIVATION

I encountered this while using statrs in a Leptos application targeting
wasm32-unknown-unknown.

Seeded sampling should not require a host entropy source, while browser
applications using APIs such as rand::rng() need an explicit JavaScript
entropy backend.

This PR separates these use cases: the regular rand feature supports seeded
RNGs without enabling host entropy, while the new opt-in wasm_js feature
enables JavaScript-backed randomness.

Changes

• Update rand from 0.9 to 0.10.
• Update nalgebra from 0.34 to 0.35 to keep its rand integration compatible.
• Migrate sampling implementations to the rand 0.10 RngExt API.
• Use nalgebra/rand-no-std to avoid implicitly enabling thread_rng.
• Enable rand/std_rng for explicitly seeded RNGs without requiring
  getrandom.
• Add the opt-in wasm_js feature, enabling:
  • rand/thread_rng
  • getrandom/wasm_js
• Add CI checks for:
  • wasm32-unknown-unknown with seeded RNG support
  • wasm32-unknown-unknown with wasm_js
  • wasm32-wasip1
• Update examples, benchmarks, documentation, and the MSRV lockfile.
• Increase MSRV from 1.87 to 1.89, as required by nalgebra 0.35.

Acknowledgements

Thanks to @RobertJacobsonCDC for the earlier rand 0.9 migration in #331,
@qkniep for the work on the rand 0.10 migration in #374

[day01]

Previously, both benchmarks almost always measured the fast path returning NaN instead of the intended selection algorithms.

[codecov]

Codecov Report

❌ Patch coverage is 64.70588% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.41%. Comparing base (75303bb) to head (7df8f81).

Files with missing lines	Patch %	Lines
src/generate.rs	0.00%	4 Missing ⚠️
src/distribution/dirichlet.rs	0.00%	1 Missing ⚠️
src/distribution/multivariate_normal.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #384      +/-   ##
==========================================
+ Coverage   94.39%   94.41%   +0.01%     
==========================================
  Files          59       59              
  Lines       12982    12990       +8     
==========================================
+ Hits        12254    12264      +10     
+ Misses        728      726       -2     

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[day01]

I don't think so coverage on display is necessary, but if you req that @YeungOnion i will add...