Optimisation of Shannon Entropy function

[nikdon]

• Version for string inputs uses Counter to improve performance
• Version for non-string
  • Uses np.unique with the return_counts=True parameter to directly obtain unique values and their corresponding counts from the time series array.
  • Utilizes NumPy's array operations to calculate frequencies and perform element-wise multiplication and summation without explicit loops.

Benchamrk:

Size	Original Time	Efficient Time (string)	Efficient Time (non-string)	Efficient (string) vs Original, % diff	Efficient (non-string) vs Original, % diff
10	0.000839	0.000605	0.001009	27.89%	-20.26%
100	0.033200	0.004940	0.001059	85.12%	96.81%
500	0.486557	0.022725	0.001692	95.33%	99.65%
1000	1.882986	0.046219	0.002610	97.55%	99.86%