Add From<Infallible> impl for PanicReason (#36)

Some implementations in the interpreter benefir from the standard lib
`Infallible` implementation for errors that won't ever happen, except
for critical OS failures that are beyond the runtime control scope.

PanicReason should derive an implementation of infallible, and panic in
case it is ever reached.

fuel-asm/src/panic_reason.rs

@@ -1,4 +1,4 @@
-use core::fmt;
+use core::{convert, fmt};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 #[cfg_attr(
@@ -534,3 +534,9 @@ impl std::error::Error for PanicReason {
  None
  }
 }
+
+impl From<convert::Infallible> for PanicReason {
+ fn from(_i: convert::Infallible) -> Self {
+ unreachable!()
+ }
+}