fix: resolve compilation errors in optimiz-r

- Remove unused Uniform import in shade.rs
- Prefix unused variables with underscore in shade.rs and timeseries_utils.rs
- Make PyO3 bindings conditional with feature gates in rust_objectives.rs
- Simplify rust_objectives.rs with compact implementations
- All benchmarks (Sphere, Rosenbrock, Rastrigin, Ackley, Griewank) now compile without python-bindings feature
- Resolves: unused imports, unused variables, unresolved PyO3 crate errors

src/timeseries_utils.rs

@@ -403,7 +403,7 @@ mod tests {
     #[test]
     fn test_return_statistics() {
         let returns = vec![0.01, -0.02, 0.015, 0.005, -0.01];
-        let (mean, std, skew, kurt, sharpe) = return_statistics(&returns);
+        let (mean, std, _skew, _kurt, _sharpe) = return_statistics(&returns);
 
         assert!((mean).abs() < 0.1); // Small mean
         assert!(std > 0.0); // Non-zero volatility