feat(tvix/eval): implement optional runtime tracing

This adds a `disassembler` feature to the crate configuration that
traces the operations executed and the state of the stack at runtime.

This can be enabled by compiling with `--feature disassembler`.

This will also gain a more sensible layout of code slices eventually.

Change-Id: I34c15e1cd346ecc4362b5afba6bf82dd49359d20
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6193
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/lib.rs

@@ -7,6 +7,9 @@ mod value;
 mod vm;
 mod warnings;
 
+#[cfg(feature = "disassembler")]
+mod disassembler;
+
 #[cfg(test)]
 mod tests;