Remove distinction between regex and string match key

[ASEM000]

import sepes as sp

params = {
    "a_1": 1,
    "a_2": 2,
    "c": 3,
}

# new way: use regex pattern directly
sp.at(params)["a_.*"].set(10) # {'a_1': 10, 'a_2': 10, 'c': 3}

# old deprecated way: use re.compile + pattern
import re
sp.at(params)[re.compile("a_.*")].set(10) # {'a_1': 10, 'a_2': 10, 'c': 3}

This change is motivated by serket, keras, and recently grok

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.15385% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 94.57%. Comparing base (5da1685) to head (9f26b58).

Files	Patch %	Lines
tests/test_index.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next      #14      +/-   ##
==========================================
+ Coverage   94.33%   94.57%   +0.23%     
==========================================
  Files          13       13              
  Lines        2332     2304      -28     
==========================================
- Hits         2200     2179      -21     
+ Misses        132      125       -7     

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