Small optimisations

[hugovk]

Some small optimisations, won't make a huge amount of difference due to the heavy importlib import:

• Exit early before parsing emoji
• Only import json and random if needed
• Replace re.sub() with str.replace()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.54%. Comparing base (6bb70de) to head (353b1d7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #159      +/-   ##
==========================================
- Coverage   95.58%   95.54%   -0.05%     
==========================================
  Files           2        2              
  Lines         204      202       -2     
==========================================
- Hits          195      193       -2     
  Misses          9        9              

Flag	Coverage Δ
macos-latest	92.57% <100.00%> (-0.08%)	⬇️
ubuntu-latest	93.06% <100.00%> (-0.07%)	⬇️
windows-latest	92.57% <100.00%> (-0.08%)	⬇️

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