Improve the fetcher revision API (#193)

* Convert Revision to u32

* Parse revision

* Narrow revision parsing error type

chromiumoxide_fetcher/src/revision.rs

@@ -1,6 +1,4 @@
-use std::fmt;
-
-use crate::FetcherError;
+use std::{fmt, num::ParseIntError};
 
 /// A [`Revision`] represents a version of chromium.
 ///
@@ -16,14 +14,25 @@ impl From<u32> for Revision {
     }
 }
 
+impl From<Revision> for u32 {
+    fn from(value: Revision) -> Self {
+        value.0
+    }
+}
+
+impl std::str::FromStr for Revision {
+    type Err = ParseIntError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        s.parse::<u32>().map(|v| Self(v))
+    }
+}
+
 impl TryFrom<String> for Revision {
-    type Error = FetcherError;
+    type Error = ParseIntError;
 
     fn try_from(value: String) -> Result<Self, Self::Error> {
-        value
-            .parse::<u32>()
-            .map_err(|e| FetcherError::InvalidRevision(e))
-            .map(|v| Self(v))
+        value.parse()
     }
 }