S3.1 — Rust core: edition 2024, rand 0.10, getrandom 0.4

Intent

Bring the oxmpl core onto current Rust dependencies so everything downstream (bindings, CI, 0.9.0 validation work) starts from the new rand API. Breaking for Rust users who implement StateSpace or Goal (public traits expose &mut impl Rng).

Acceptance criteria

• Workspace on edition 2024; rust-version = "1.85" declared for all crates
• rand 0.10 + getrandom 0.4 (wasm_js feature retained); unused rand_chacha removed
• Seeded-RNG guard tests (oxmpl/tests/seeded_rng_tests.rs) pass unchanged — confirms StdRng output stability across the upgrade
• oxmpl-py and oxmpl-js compile against the new core (compile fixes only)
• just test-all green; clippy -D warnings clean

Tasks

• Edition 2024 migration across the workspace (cargo fix --edition)
• Rng → RngExt (~40 uses); dyn RngCore → dyn Rng (5); StdRng::from_os_rng() → rand::make_rng() (5 planner sites)
• Remove rand_chacha from oxmpl/Cargo.toml
• Fix binding compile errors from the renames (goal adapters' sample_goal)
• Commit carries a BREAKING CHANGE: footer (rand trait rename)

Completion (2026-10-09)

Commit 08dadb6 on branch toolchain-refresh (originally a79e10f; rewritten before push): build(deps)!: move to edition 2024, rand 0.10 and getrandom 0.4.

Evidence (run on the staged snapshot; HEAD re-checked for fmt):

• Edition 2024 + rust-version = "1.85" inherited from the workspace root in all 4 crates (confirmed via cargo metadata).
• Lock: rand 0.10.3, rand_core 0.10.1, getrandom 0.4.3; rand_chacha gone.
• Rust tests 91 passed / 0 failed, including all 5 seeded-RNG guard tests (only change to that file: the RngExt import).
• Python 34/34, JS (wasm-pack + vitest) 30/30 — the three parts of just test-all, run individually.
• cargo clippy --workspace --all-targets -- -D warnings clean; cargo fmt --all --check clean at HEAD.
• oxmpl-js builds for wasm32-unknown-unknown.

Folded in (same code, no new story): RngWrapper adaptor in any_state_space.rs deleted (rand 0.10 makes &mut dyn Rng an Rng); .cargo/config.toml deleted (the getrandom_backend="wasm_js" flag is a no-op since getrandom 0.3.4; WASM build + vitest verified without it).

Notes:

• The BREAKING CHANGE: footer names the rand trait rename but not the MSRV raise to 1.85. Acceptable for the AC; mention MSRV in the 0.8.0 release notes (S3.6).
• just test-all was not run as the recipe itself: the shell's VIRTUAL_ENV pointed at the deleted ~/Documents/casual/oxmpl/.venv. Re-entering the worktree (direnv) fixes it.