Fix tool calling (#1529)

## Motivation

GPT OSS tool calling issues.

## Changes

Fixes those and adds a bunch of evals for tool calling.
Fixes GLM5 prefix caching, where CacheList wasn't getting handled
properly.
Extracts a bunch of the setup functionality of exo bench to a harness
that can be reused elsewhere, such as in the tool calling eval.

## Test Plan
### Automated Testing
Let's run the evals for all models

python/parts.nix

@@ -158,6 +158,7 @@
           exo-test-env = testVenv;
         } // {
         exo-bench = mkBenchScript "exo-bench" (inputs.self + /bench/exo_bench.py);
+        exo-eval-tool-calls = mkBenchScript "exo-eval-tool-calls" (inputs.self + /bench/eval_tool_calls.py);
         exo-get-all-models-on-cluster = mkSimplePythonScript "exo-get-all-models-on-cluster" (inputs.self + /tests/get_all_models_on_cluster.py);
       };