Make std optional

Cargo.toml

@@ -17,4 +17,6 @@ num-traits = "0.2"
 defmt = { version = "0.3", optional = true }
 
 [features]
+default = ["std"]
 defmt = ["dep:defmt"]
+std = []

src/display.rs

@@ -1,3 +1,6 @@
+#[cfg(not(feature = "std"))]
+use core::fmt::{Display, Formatter};
+#[cfg(feature = "std")]
 use std::fmt::{Display, Formatter};
 
 use typenum::Integer;

src/lib.rs

@@ -1,6 +1,15 @@
 mod display;
 pub mod types;
 
+#[cfg(not(feature = "std"))]
+use core::{
+    marker::PhantomData,
+    ops::{
+        Add, AddAssign, Deref, DerefMut, Div, DivAssign, Mul, MulAssign, Neg, Rem, RemAssign, Sub,
+        SubAssign,
+    },
+};
+#[cfg(feature = "std")]
 use std::{
     marker::PhantomData,
     ops::{