test(tazjin/rlox): Add some tests for numerical operations

If I was adding any dependencies, this might be a good one for a
property-based test thing, but I'm not going to.

Change-Id: Ia801d041479d1a88c59ef9e0fe1460b3640382e3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2569
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

users/tazjin/rlox/src/bytecode/mod.rs

@@ -9,6 +9,9 @@ mod opcode;
 mod value;
 mod vm;
 
+#[cfg(test)]
+mod tests;
+
 use chunk::Chunk;
 pub struct Interpreter {}