chore(rust): bump rand 0.8 -> 0.10, rand_xoshiro 0.6 -> 0.8

These two crates are coupled through rand_core and must move together;
rand_xoshiro 0.8 requires the rand_core that ships with rand 0.9+.

API churn handled in bootstrap.rs (rand 0.9 renamed the gen* family):
- rng.gen::<bool>()    -> rng.random::<bool>()
- rng.gen::<f64>()     -> rng.random::<f64>()
- rng.gen_range(0..6)  -> rng.random_range(0..6)

Bit-identity preserved: Xoshiro256PlusPlus::seed_from_u64(seed) produces
the same byte stream in 0.6 and 0.8, so existing bootstrap baselines
remain valid. Verified locally on macOS Accelerate:
- tests/test_rust_backend.py: 95 passed (includes Rust<->Python parity
  tests on bootstrap weights and bootstrap-derived SE/CI quantiles)
- Bootstrap-focused sweep across the broader test suite: 372 passed
- 467 total passing across the directly affected surfaces

Supersedes igerber#382 (rand) and igerber#384 (rand_xoshiro). blas-src 0.10 -> 0.14
(igerber#386) deferred pending an ndarray compatibility check; out of scope.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: igerber

rust/Cargo.toml

@@ -25,8 +25,8 @@ openblas = ["ndarray/blas"]
 pyo3 = "0.28"
 numpy = "0.28"
 ndarray = { version = "0.17", features = ["rayon"] }
-rand = "0.8"
-rand_xoshiro = "0.6"
+rand = "0.10"
+rand_xoshiro = "0.8"
 rayon = "1.8"
 
 # Pure Rust linear algebra for SVD/matrix inversion (no external deps).

rust/src/bootstrap.rs

@@ -67,7 +67,7 @@ fn generate_rademacher_batch(n_bootstrap: usize, n_units: usize, seed: u64) -> A
         .for_each(|(i, mut row)| {
             let mut rng = Xoshiro256PlusPlus::seed_from_u64(seed.wrapping_add(i as u64));
             for elem in row.iter_mut() {
-                *elem = if rng.gen::<bool>() { 1.0 } else { -1.0 };
+                *elem = if rng.random::<bool>() { 1.0 } else { -1.0 };
             }
         });
 
@@ -102,7 +102,7 @@ fn generate_mammen_batch(n_bootstrap: usize, n_units: usize, seed: u64) -> Array
         .for_each(|(i, mut row)| {
             let mut rng = Xoshiro256PlusPlus::seed_from_u64(seed.wrapping_add(i as u64));
             for elem in row.iter_mut() {
-                *elem = if rng.gen::<f64>() < prob_neg {
+                *elem = if rng.random::<f64>() < prob_neg {
                     val_neg
                 } else {
                     val_pos
@@ -142,7 +142,7 @@ fn generate_webb_batch(n_bootstrap: usize, n_units: usize, seed: u64) -> Array2<
             let mut rng = Xoshiro256PlusPlus::seed_from_u64(seed.wrapping_add(i as u64));
             for elem in row.iter_mut() {
                 // Uniform selection: generate integer 0-5, index into weights_table
-                let bucket = rng.gen_range(0..6);
+                let bucket = rng.random_range(0..6);
                 *elem = weights_table[bucket];
             }
         });