fix: compile error when using enum in flutter

libs/flutter_rust_bridge_codegen/src/error.rs

@@ -0,0 +1,32 @@
+use thiserror::Error;
+
+pub type Result = std::result::Result<(), Error>;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("rustfmt failed: {0}")]
+    Rustfmt(String),
+    #[error("dart fmt failed: {0}")]
+    Dartfmt(String),
+    #[error(
+        "ffigen could not find LLVM.
+    Please supply --llvm-path to flutter_rust_bridge_codegen, e.g.:
+    
+        flutter_rust_bridge_codegen .. --llvm-path <path_to_llvm>"
+    )]
+    FfigenLlvm,
+    #[error("{0} is not a command, or not executable.")]
+    MissingExe(String),
+    #[error("{0}")]
+    StringError(String),
+}
+
+impl Error {
+    pub fn str(msg: &str) -> Self {
+        Self::StringError(msg.to_owned())
+    }
+
+    pub fn string(msg: String) -> Self {
+        Self::StringError(msg)
+    }
+}