fix: Clean up unused imports and variables in mean_field modules

- Remove unused OptimizrError imports in pde_solvers and mod.rs
- Remove unused Array2 import in optimal_transport.rs
- Remove unused Grid and pde_solvers imports in nash_equilibrium.rs
- Fix m_new variable declaration in forward_backward.rs
- Add #[allow(non_snake_case)] for T field/parameter in python_bindings.rs
- Prefix unused hist_cr variable in shade.rs

All changes fix compilation warnings while preserving functionality.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "optimizr"
-version = "0.2.0"
+version = "0.3.0"
 description = "High-performance optimization algorithms in Rust with Python bindings"
 authors = [
     {name = "Your Name", email = "your.email@example.com"}