revert(tvix/eval): Don't double-box Path values

This reverts commit d3d41552cf.

This was well-intentioned, but now the boxed Path values are actually
the *largest* Value enum variants, at 16 bytes (because they're
fat-pointers, with a len) instead of 8 bytes like all the other values.
Having the double reference is a reasonable price to pay (it seems; more
benchmarks may end up disagreeing) for a smaller Value repr.

Change-Id: I0d3e84f646c8f5ffd0b7259c4e456637eea360f7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10797
Tested-by: BuildkiteCI
Autosubmit: aspen <root@gws.fyi>
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/value/json.rs

@@ -27,7 +27,7 @@ impl Value {
             Value::String(s) => Json::String(s.to_str()?.to_owned()),
 
             Value::Path(p) => {
-                let imported = generators::request_path_import(co, p.into_path_buf()).await;
+                let imported = generators::request_path_import(co, *p).await;
                 Json::String(imported.to_string_lossy().to_string())
             }