Learner1D type hints and add typeguard to pytest tests

[basnijholt]

Description

I am splitting up #244 into smaller parts.

Since it has been ready for review for almost 2 years but no-one has looked at it, I will go ahead and auto-complete this as soon as the typeguard and mypy issues have been solved.

Checklist

• Fixed style issues using pre-commit run --all (first install using pip install pre-commit)
• pytest passed

Type of change

Check relevant option(s).

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• (Code) style fix or documentation update
• This change requires a documentation update

[codecov-commenter]

Codecov Report

Merging #325 (087a00f) into master (c820704) will increase coverage by 0.04%.
The diff coverage is 97.46%.

@@            Coverage Diff             @@
##           master     #325      +/-   ##
==========================================
+ Coverage   80.72%   80.77%   +0.04%     
==========================================
  Files          38       38              
  Lines        5018     5045      +27     
  Branches      918      918              
==========================================
+ Hits         4051     4075      +24     
- Misses        822      824       +2     
- Partials      145      146       +1     

Impacted Files	Coverage Δ
adaptive/learner/learner1D.py	90.15% <97.22%> (+0.41%)	⬆️
adaptive/learner/average_learner1D.py	78.88% <100.00%> (-0.75%)	⬇️
adaptive/learner/base_learner.py	84.09% <100.00%> (ø)
adaptive/tests/test_learners.py	98.83% <100.00%> (+<0.01%)	⬆️

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