Add type-hints to SKOptLearner

[basnijholt]

Description

Please include a summary of the change and which (if so) issue is fixed.

Fixes #(ISSUE_NUMBER_HERE)

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 #376 (7de89c8) into main (1b7e84d) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@ Coverage Diff @@ ## main #376 +/- ## ========================================== + Coverage 77.67% 77.69% +0.02%  ========================================== Files 37 37 Lines 5393 5394 +1 Branches 981 981 ========================================== + Hits 4189 4191 +2  Misses 1058 1058 + Partials 146 145 -1 

Impacted Files	Coverage Δ
adaptive/learner/skopt_learner.py	60.00% <100.00%> (+0.57%)	⬆️
adaptive/learner/learner1D.py	87.16% <0.00%> (-0.50%)	⬇️
adaptive/learner/learnerND.py	59.10% <0.00%> (+0.37%)	⬆️
adaptive/tests/test_cquad.py	92.25% <0.00%> (+0.64%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more