chore: Sphinx version pin, refactor config to set appropriate default (#68)

[SecondSkoll]

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 16.55%. Comparing base (5a4416e) to head (31b62c9).
⚠️ Report is 65 commits behind head on main.

Files with missing lines	Patch %	Lines
canonical_sphinx/config.py	0.00%	2 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (5a4416e) and HEAD (31b62c9). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (5a4416e)	HEAD (31b62c9)
	3	1

Additional details and impacted files

@@             Coverage Diff              @@
##              main      #97       +/-   ##
============================================
- Coverage   100.00%   16.55%   -83.45%     
============================================
  Files            1        3        +2     
  Lines           10      145      +135     
  Branches         2       24       +22     
============================================
+ Hits            10       24       +14     
- Misses           0      121      +121     

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