Refactor: Implement Display trait and improve code quality

[kyluke]

Summary

This PR refactors the codebase to implement Rust's Display trait for better idiomatic string conversion, improves code quality through various clippy suggestions, and makes numerous small improvements to code clarity and maintainability.

Key Changes

Display Trait Implementation

• Model enum: Replaced custom to_string() method with std::fmt::Display implementation, removing unnecessary .to_owned() calls
• Verbosity enum: Replaced custom to_string() method with Display trait implementation
• Role enum: Replaced custom to_string() method with Display trait implementation

Default Trait Improvements

• Verbosity enum: Converted to use #[derive(Default)] with #[default] attribute instead of manual implementation
• MessageType enum: Converted to use #[derive(Default)] with #[default] attribute
• PresetConfig struct: Converted to use #[derive(Default)] instead of manual implementation
• PreambleConfig struct: Converted to use #[derive(Default)] instead of manual implementation

Code Quality & Idiom Improvements

• Replaced map_err(|e| function(e)) with map_err(function) for cleaner error handling
• Replaced starts_with() checks with strip_prefix() for more idiomatic string handling
• Replaced filter_map() with map() where filtering logic was unnecessary
• Replaced .min(1.0).max(0.0) with .clamp(0.0, 1.0) for range clamping
• Replaced map_or(false, ...) with is_ok_and() and is_some_and() for better readability
• Replaced vec![...] with array literals [...] where appropriate
• Simplified conditional logic by removing unnecessary nesting
• Replaced &format!(...) with format!(...) where reference wasn't needed
• Replaced format_args!(...).to_string() with direct string formatting

Documentation & Comments

• Converted doc comments (///) to regular comments (//) for module-level documentation where appropriate
• Improved comment formatting consistency

Minor Fixes

• Removed unused imports (e.g., use chrono;)
• Added #[allow(clippy::too_many_arguments)] attributes where needed
• Added #[allow(clippy::module_inception)] attribute
• Replaced "\n" with '\n' for single character strings
• Simplified pattern matching with if let and or_else() chains
• Improved variable naming and clarity in several functions

Implementation Details

• All changes maintain backward compatibility and functionality
• The refactoring prioritizes idiomatic Rust patterns and compiler suggestions
• String conversion now leverages Rust's standard Display trait for consistency
• Error handling is more concise while maintaining clarity

https://claude.ai/code/session_01J96NRV6o9dKTmr7igJmcaG