chore(git): enhance rust diffing

This has to be explicitly enabled for git to utilize its enhanced rust diffing, evidently. 

ref: rust-lang/rust#78882

Author: sambacha

.gitattributes

@@ -1,2 +1,5 @@
 crates/cheatcodes/assets/*.json linguist-generated
 testdata/cheats/Vm.sol linguist-generated
+
+# See <https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header>
+*.rs diff=rust