🔧 Enforce type checking in api/need.py

[chrisjsewell]

Note, I have made changes in a way to not breaking any existing logic / tests.
However, I've added a number of TODOs where I have "ignored" type incompatibilities that do look like they should be resolved.

For example, add_external_need, understandably sets docname/lineno to None, however, some parts of the code base appear to not account for this possibility.

Anyway, I'll look into these in later PRs

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (aef3a0f) 85.82% compared to head (b2d6c85) 85.82%.

Files	Patch %	Lines
sphinx_needs/api/need.py	95.65%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1117      +/-   ##
==========================================
- Coverage   85.82%   85.82%   -0.01%     
==========================================
  Files          56       56              
  Lines        6506     6503       -3     
==========================================
- Hits         5584     5581       -3     
  Misses        922      922              

Flag	Coverage Δ
pytests	85.82% <97.43%> (-0.01%)	⬇️

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