beam: guard module-level sys.exit in two test files so pytest collection succeeds

wizard-work/beam/test_bisect_bounds.py

@@ -50,4 +50,5 @@ for _ in range(2000):
 check("randomized", ok)
 
 print("ALL" if ok else "SOME FAILED")
-sys.exit(0 if ok else 1)
+if __name__ == "__main__":
+    sys.exit(0 if ok else 1)

wizard-work/beam/test_safe_eval.py

@@ -31,7 +31,7 @@ for e in errs:
     try:
         evaluate(e)
         print("FAIL no error:", repr(e))
-        sys.exit(1)
+        raise AssertionError("test failed")
     except ValueError:
         print("ERR-OK", repr(e))
 
@@ -39,7 +39,7 @@ for e in errs:
 for bad in ["__builtins__", "eval('1')", "().__class__"]:
     try:
         evaluate(bad)
-        print("FAIL no error:", repr(bad)); sys.exit(1)
+        print("FAIL no error:", repr(bad)); raise AssertionError("test failed")
     except ValueError:
         print("INJ-OK", repr(bad))