Keyword-only arguments for a bunch of internal methods

[simonw]

Refs #1822

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📚 Documentation preview 📚: https://datasette--1823.org.readthedocs.build/en/1823/

[simonw]

I should update the documentation to reflect this change.

[simonw]

Also need to do a bit more of an audit to see if there is anywhere else that this style should be applied.

[codecov]

Codecov Report

Base: 91.58% // Head: 92.50% // Increases project coverage by +0.91% 🎉

Coverage data is based on head (b545b6a) compared to base (5f9f567).
Patch coverage: 90.47% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1823      +/-   ##
==========================================
+ Coverage   91.58%   92.50%   +0.91%     
==========================================
  Files          36       35       -1     
  Lines        4444     4400      -44     
==========================================
  Hits         4070     4070              
+ Misses        374      330      -44     

Impacted Files	Coverage Δ
datasette/utils/asgi.py	91.06% <88.23%> (ø)
datasette/app.py	94.11% <100.00%> (ø)
datasette/utils/shutil_backport.py

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