feat(tvix/castore): impl Debug for B3Digest

Use the same format as Display, b3: followed by the base64
representation. This makes the debug implementation of everything
containing a b3 digest much nicer to read.

Change-Id: I3ca3154d0b6fb07781c8f9c83ece3ff1a6957902
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11181
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/castore/src/digests.rs

@@ -2,7 +2,7 @@ use bytes::Bytes;
 use data_encoding::BASE64;
 use thiserror::Error;
 
-#[derive(PartialEq, Eq, Hash, Debug)]
+#[derive(PartialEq, Eq, Hash)]
 pub struct B3Digest(Bytes);
 
 // TODO: allow converting these errors to crate::Error
@@ -78,3 +78,9 @@ impl std::fmt::Display for B3Digest {
         write!(f, "b3:{}", BASE64.encode(&self.0))
     }
 }
+
+impl std::fmt::Debug for B3Digest {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "b3:{}", BASE64.encode(&self.0))
+    }
+}