fix: import rand distributions from ndarray_rand::rand_distr to fix E0277 trait-bound (#55)

## Why

Both `crates/esn/src/lib.rs` and `crates/lsm/src/lib.rs` import
`Normal`, `Uniform`, `Bernoulli` from the top-level `rand_distr` crate,
then pass those distribution instances to:

- `Array2::random_using(...)` from `ndarray_rand::RandomExt`, which
requires `ndarray_rand::rand_distr::Distribution`
- `rng.sample(...)` which works fine with either

`ndarray-rand` re-exports its own pinned version of `rand_distr` and the
`RandomExt::random_using` trait bound is over that re-exported
`Distribution`. When the top-level `rand_distr` version drifts
(Dependabot bump), it stops being the same type as
`ndarray_rand::rand_distr::Distribution` and the trait bound fails:

```
error[E0277]: the trait bound `rand_distr::Normal<{float}>: ndarray_rand::rand_distr::Distribution<_>` is not satisfied
```

…on every Dependabot PR that touched the `rand` family.

## Fix

Import distributions through `ndarray_rand::rand_distr` so the version
always matches the trait bound. No runtime / behaviour change.

## Tested

Static: rg confirms `Normal`/`Uniform`/`Bernoulli` are only used through
`rng.sample()` and `Array2::random_using()`, both of which accept the
ndarray_rand::rand_distr versions.

After this lands, the workspace's top-level `rand_distr` dep may be
unused — left in place to avoid scope creep; can drop in a follow-up if
cargo-udeps flags it.

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: hyperpolymath

crates/esn/src/lib.rs

@@ -14,7 +14,7 @@
 use ndarray::{Array1, Array2};
 use ndarray_rand::RandomExt;
 use rand::Rng;
-use rand_distr::{Normal, Uniform};
+use ndarray_rand::rand_distr::{Normal, Uniform};
 use serde::{Deserialize, Serialize};
 use std::collections::VecDeque;
 use thiserror::Error;

crates/lsm/src/lib.rs

@@ -9,7 +9,7 @@
 use ndarray::{Array1, Array2, Axis};
 use ndarray_rand::RandomExt;
 use rand::Rng;
-use rand_distr::{Bernoulli, Normal, Uniform};
+use ndarray_rand::rand_distr::{Bernoulli, Normal, Uniform};
 use serde::{Deserialize, Serialize};
 use std::collections::VecDeque;
 use thiserror::Error;