[Fix] Update plotting imports and thread handling in Pepper class (#382)

- plt.subplot does not work reliably with async/ threads.
- Bug in thread run that would fail with env set (string to number)

Reviewed-on: enviPath/enviPy#382
Co-authored-by: Tobias O <tobias.olenyi@envipath.com>
Co-committed-by: Tobias O <tobias.olenyi@envipath.com>

pepper/impl/pepper.py

@@ -187,8 +187,9 @@ class Pepper:
         groups = [group for group in dataset.group_by("structure_id")]
 
         # Unless explicitly set compute everything serial
-        if os.environ.get("N_PEPPER_THREADS", 1) > 1:
-            results = Parallel(n_jobs=os.environ["N_PEPPER_THREADS"])(
+        n_threads = int(os.environ.get("N_PEPPER_THREADS", 1))
+        if n_threads > 1:
+            results = Parallel(n_jobs=n_threads)(
                 delayed(compute_bayes_per_group)(group[1])
                 for group in dataset.group_by("structure_id")
             )