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

@@ -14,7 +14,6 @@ from __future__ import annotations
 import re
 import sys
 from typing import Union
-from typing_extensions import Literal
 
 import numba as nb
 import numpy as np
@@ -23,6 +22,7 @@ import pandas as pd
 from scipy.signal import butter, filtfilt
 from scipy.stats import iqr, median_abs_deviation
 from sklearn.neighbors import NearestNeighbors
+from typing_extensions import Literal
 
 from saqc.lib.tools import getFreqDelta