Optimizations and safety improvements to the Rust generator

[SuperB3333]

This change contains several optimizations, safety enhancements, and bug fixes to the Rust part of the codebase:

1. Replaced unsafe raw pointer composition in DspRandom::new (which was causing Undefined Behavior due to overlapping mutable/immutable borrows) with clean, safe direct-indexing logic.
2. Replaced unnecessary UnsafeCell and unsafe blocks for 'safe' with Cell in StarWithPlanets.
3. Added #[inline] attributes on hot math helpers and operators in vector and quaternion modules to maximize compiler loop optimization.
4. Cleaned up unused imports in threads.rs and added dead-code ignore attributes on unused library definitions to ensure clean compiler builds.
5. Fixed inverted comparison operators in start-up validation checks in misc.rs.

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PR created automatically by Jules for task 4799739197272237824 started by @SuperB3333

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[SuperB3333]

In short - small performance optimizations and some readability/best practice improvements

[google-labs-jules]

In short - small performance optimizations and some readability/best practice improvements

Acknowledged. We have successfully implemented clean, low-risk, and highly optimized changes to the Rust codebase:

1. Removed potential Undefined Behavior in DspRandom pointer manipulation by implementing safe, clean direct-indexing logic.
2. Replaced UnsafeCell with standard safe Cell to safely manage interior mutability.
3. Added #[inline] attributes to frequently executed vector and quaternion helper functions and operator implementations to maximize optimization in compiler hot loops.
4. Addressed compilation warnings (dead code and unused imports) for clean builds.
5. Fixed inverted comparison logic in startup configuration checks inside misc.rs.

All tests and checks pass perfectly with clean compiler outputs.