Also use alloc feature in formatter

Cargo.toml

@@ -26,7 +26,7 @@ default = ["std", "full-decoder", "formatter"]
 alloc = []
 std = ["alloc"]
 full-decoder = []
-formatter = ["std", "full-decoder"]
+formatter = ["alloc", "full-decoder"]
 encoder = ["alloc", "full-decoder"]
 serialization = ["serde", "bitflags/serde"]
 nolibc = []

src/encoder.rs

@@ -719,6 +719,7 @@ macro_rules! insn32 {
 #[cfg(all(test, feature = "formatter"))]
 mod tests {
     use super::*;
+    use alloc::string::ToString as _;
 
     #[test]
     fn insn_macro() {

src/formatter.rs

@@ -1,9 +1,10 @@
 //! Textual instruction formatting routines.
 
+use alloc::{borrow::ToOwned, boxed::Box, string::String};
 use core::{
+    ffi::{c_void, CStr},
     fmt,
     mem::{self, MaybeUninit},
-    ffi::{c_void, CStr},
     ptr,
 };