chore: update rand crate to 0.10.1 (#492)

## What changed
- Updated `rand` to `0.10.1` in both workspace crates
- Regenerated `Cargo.lock` for the new dependency graph
- Migrated code to the `rand 0.10` APIs:
  - `thread_rng` -> `rng`
  - `distributions` -> `distr`
  - `OsRng` -> `SysRng` for local random byte generation
  - `fill` -> `try_fill_bytes` with explicit error handling
- Kept RSA encryption compatibility by using `rsa::rand_core::OsRng`
- Restored deterministic `steamguard` test RNG behavior with a `rand
0.8` dev dependency alias (`rand_08`) for the existing StepRng based
test vectors

## Validation
- `cargo test`
- `cargo test -p steamguard`

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