refactor: address clippy warnings and improve code quality (#409)

- Fix string formatting with modern interpolation syntax
- Improve Debug implementation with finish_non_exhaustive()
- Fix function placement in shape.rs to avoid items_after_statements warning
- Use more idiomatic Rust patterns (map_or_else, next_back)
- Clean up conditional imports in vi.rs
- Convert multiple methods to `const` functions for optimization and consistency
- Introduce `core_maths` for enhanced no-std compatibility
- Update `Cargo.toml` for the new optional dependency and feature adjustments

src/edit/vi.rs

@@ -1,7 +1,6 @@
-#[cfg(feature = "no_std")]
-use core::cmp;
-
 use alloc::{collections::BTreeMap, string::String};
+#[cfg(feature = "swash")]
+use core::cmp;
 use modit::{Event, Key, Parser, TextObject, WordIter};
 
 use crate::{