feat: add #[non_exhaustive] to error enums

Marks DecodeError and EncodeError as #[non_exhaustive] to allow adding
new error variants in future versions without breaking downstream code.

This is a semver best practice for public error enums, as it forces
downstream users to include a wildcard arm in match expressions.

Closes #179

Author: lilith

jpegxl-rs/src/errors.rs

@@ -23,6 +23,7 @@ use jpegxl_sys::{decode::JxlDecoderStatus, encoder::encode::JxlEncoderError};
 
 /// Errors derived from [`JxlDecoderStatus`]
 #[derive(Error, Debug)]
+#[non_exhaustive]
 pub enum DecodeError {
     /// Cannot create a decoder
     #[error("Cannot create a decoder")]
@@ -50,6 +51,7 @@ pub enum DecodeError {
 /// Errors derived from [`JxlEncoderStatus`][jpegxl_sys::encoder::encode::JxlEncoderStatus]
 /// and [`JxlEncoderError`]
 #[derive(Error, Debug)]
+#[non_exhaustive]
 pub enum EncodeError {
     /// Cannot create an encoder
     #[error("Cannot create an encoder")]