feat(tvix/build): add BuildRequest validation

Change-Id: I8182e4c4a7e5694c1e6f1f56ce092751c22adf4c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10538
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/glue/src/tvix_build.rs

@@ -141,7 +141,7 @@ where
         provide_bin_sh: true,
     });
 
-    Ok(BuildRequest {
+    let build_request = BuildRequest {
         command_args,
         outputs: output_paths,
 
@@ -161,7 +161,15 @@ where
                 .into_iter()
                 .map(|(path, contents)| AdditionalFile { path, contents }),
         ),
-    })
+    };
+
+    debug_assert!(
+        build_request.validate().is_ok(),
+        "invalid BuildRequest: {}",
+        build_request.validate().unwrap_err()
+    );
+
+    Ok(build_request)
 }
 
 /// handle passAsFile, if set.