Performance tweaks for to_camel_case

[pamelafox]

This PR includes two performance tweaks for the to_camel_case function:

1) It replaces the generator expression passed to str.join() with a list comprehension. The list comprehension is actually 10-15% faster as str.join() turns its arguments into a list anyway (if they're not already). More details in this benchmark test: https://github.com/tonybaloney/anti-patterns/pull/4

2) It removes the re.IGNORECASE flag and instead specifies a-zA-Z instead of a-z. That seems to be 20-25% faster according to benchmark in https://github.com/tonybaloney/anti-patterns/pull/5

[codecov[bot]]

Codecov Report

Merging #131 (cc1101d) into dev (6271020) will decrease coverage by 4.04%. The diff coverage is 100.00%.

:exclamation: Current head cc1101d differs from pull request most recent head e283dd1. Consider uploading reports for the commit e283dd1 to get more accurate results

@@            Coverage Diff             @@
##              dev     #131      +/-   ##
==========================================
- Coverage   90.09%   86.04%   -4.05%     
==========================================
  Files          51       50       -1     
  Lines        2959     2903      -56     
  Branches      396      391       -5     
==========================================
- Hits         2666     2498     -168     
- Misses        218      329     +111     
- Partials       75       76       +1     

Flag	Coverage Δ
unittests	86.01% <100.00%> (-4.05%)	:arrow_down:

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Impacted Files	Coverage Δ
azure/functions/decorators/utils.py	97.46% <100.00%> (ø)
azure/functions/queue.py	50.79% <0.00%> (-44.45%)	:arrow_down:
azure/functions/http.py	53.94% <0.00%> (-30.27%)	:arrow_down:
azure/functions/cosmosdb.py	74.35% <0.00%> (-25.65%)	:arrow_down:
azure/functions/eventhub.py	69.46% <0.00%> (-19.09%)	:arrow_down:
azure/functions/kafka.py	79.85% <0.00%> (-11.95%)	:arrow_down:
azure/functions/durable_functions.py	83.33% <0.00%> (-3.04%)	:arrow_down:
azure/functions/servicebus.py	83.85% <0.00%> (-2.09%)	:arrow_down:
azure/functions/_http.py	91.30% <0.00%> (-1.74%)	:arrow_down:
azure/functions/decorators/function_app.py	98.67% <0.00%> (-0.73%)	:arrow_down:
... and 4 more

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