Several fixes and refactorings to the interpolation methods

Fixes #388 (closed), unfortunately the implementation of interpolateNANs with limit is not None is quite a bit slower, then the incorrect previous one. Any ideas to speed things up are highly appreciated, I couldn't find a better solution despite a few hours of trying.

saqc/lib/ts_operators.py

@@ -13,7 +13,8 @@ from __future__ import annotations
 
 import re
 import sys
-from typing import Literal, Union
+from typing import Union
+from typing_extensions import Literal
 
 import numba as nb
 import numpy as np