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/cached.rs

@@ -11,7 +11,7 @@ pub enum Cached<T: Clone + Debug> {
 
 impl<T: Clone + Debug> Cached<T> {
     /// Gets the value if in state `Self::Used`.
-    pub fn get(&self) -> Option<&T> {
+    pub const fn get(&self) -> Option<&T> {
         match self {
             Self::Empty | Self::Unused(_) => None,
             Self::Used(t) => Some(t),
@@ -27,7 +27,7 @@ impl<T: Clone + Debug> Cached<T> {
     }
 
     /// Checks if the value is empty or unused.
-    pub fn is_unused(&self) -> bool {
+    pub const fn is_unused(&self) -> bool {
         match self {
             Self::Empty | Self::Unused(_) => true,
             Self::Used(_) => false,
@@ -35,7 +35,7 @@ impl<T: Clone + Debug> Cached<T> {
     }
 
     /// Checks if the value is used (i.e. cached for access).
-    pub fn is_used(&self) -> bool {
+    pub const fn is_used(&self) -> bool {
         match self {
             Self::Empty | Self::Unused(_) => false,
             Self::Used(_) => true,