✨🧪⬆➕ workspace, varo: Implement RNG with ChaCha8 and add optimization function

- Updated `Cargo.toml` and `Cargo.lock` to downgrade `rand_core` to 0.6.4 and add `rand_chacha` dependency with `serde1` feature.
- Implemented `Rng` struct wrapping `ChaCha8Rng` with seed initialization, stream selection, and number generation methods.
- Added `rng_new`, `rng_from_seed`, `rng_set_stream`, `rng_next_u32`, `rng_next_u64`, `rng_fill_bytes`, `rng_gen_f32`, and `rng_gen_gaussian` functions.
- Made `value` field in `Score` and `values` field in `OptimizationResult` public.
- Implemented `Distribution::sample` method that generates Gaussian numbers when moments are available.
- Added `From<f32>` implementation for `Score`.
- Implemented `optimize` function that evaluates candidates using cloned RNG streams and returns sorted results.
- Added integration test `test_optimize` that verifies optimization sorting behavior.

crates/varo/Cargo.toml

@@ -14,6 +14,7 @@ blake3.workspace = true
 vanth = { path = "../vanth" }
 vanth_derive = { path = "../vanth_derive" }
 rand_core.workspace = true
+rand_chacha.workspace = true
 
 [dev-dependencies]
 tempfile = { workspace = true }