fix(tvix/eval): fix doc comment syntax where applicable

As pointed out by grfn on cl/6091

Change-Id: I28308577b7cf99dffb4a4fd3cc8783eb9ab4d0d6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6460
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/chunk.rs

@@ -26,6 +26,9 @@ struct SourceSpan {
     count: usize,
 }
 
+/// A chunk is a representation of a sequence of bytecode
+/// instructions, associated constants and additional metadata as
+/// emitted by the compiler.
 #[derive(Clone, Debug, Default)]
 pub struct Chunk {
     pub code: Vec<OpCode>,