Introduce `ModuleLoader` to handle `#use` directives and dependency
resolution. This involves adding `tempfile` dependency, modifying
`Cargo.toml` and `Cargo.lock`, creating a new `module_loader.rs` file,
and updating `environment.rs` to use the new module.
Also, add comprehensive tests for `Diagnostics::format_errors`,
`CompilationResult`, and the new `ModuleLoader` functionality. These
tests cover various scenarios including empty diagnostics, multiple
errors, error formatting, compilation success/failure, and complex
dependency loading with topological ordering and search path resolution.
