fix(tvix/eval): gently attempt to create state dir

If the directory in which REPL history is stored does not exist,
gently try to create it, but do not raise an error if it doesn't work.

We may want to warn about it, but in general this sort of
non-essential feature should not cause a hard failure.

Change-Id: If4fe8db0c7893c39627efe72c9cd9ebf7ed63f04
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6213
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

tvix/eval/src/main.rs

@@ -42,10 +42,12 @@ fn run_prompt() {
     let mut rl = Editor::<()>::new().expect("should be able to launch rustyline");
 
     let history_path = match state_dir() {
+        // Attempt to set up these paths, but do not hard fail if it
+        // doesn't work.
         Some(mut path) => {
+            std::fs::create_dir_all(&path).ok();
             path.push("history.txt");
             rl.load_history(&path).ok();
-
             Some(path)
         }