Mark FloatType and IntegerType as #[non_exhaustive]

This is a preparation for v1.0: it's unlikely that new integer or float
types are added to the language anytime soon, but I wouldn't rule it
out. `u128` was added after all. I don't want that to cause a v2.0
release.

Author: LukasKalbertodt

src/float/mod.rs

@@ -211,6 +211,7 @@ pub(crate) fn parse_impl(input: &str) -> Result<FloatLit<&str>, ParseError> {
 
 /// All possible float type suffixes.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[non_exhaustive]
 pub enum FloatType {
     F32,
     F64,

src/integer/mod.rs

@@ -274,6 +274,7 @@ impl IntegerBase {
 
 /// All possible integer type suffixes.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[non_exhaustive]
 pub enum IntegerType {
     U8,
     U16,