Improved type hints in documentation

[JonathanWenger]

In a Nutshell

Type aliases are not properly shown in the documentation and usually expanded completely. This can make the documentation very hard to read and the typing information not very useful.

This PR uses Sphinx native functionality to display type hints instead.

Detailed Description

• Added probnum.typing to the API Documentation
• Removed plugin sphinx-autodoc-typehints
• Added Sphinx extension autodoc
• Removed colons in some commonly used classes

If a type alias still is expanded completely in the documentation the following should be added to the file:

from __future__ import annotations

Other

Note that now the new standard for documenting Parameters is to not use a colon (:).

Parameters
---------------
arg :
    Argument, where the docs may show no type hint.
betterarg
    Argument which will be documented with a type hint.

Otherwise autodoc may interpret the type of the parameter as empty.

[codecov]

Codecov Report

Merging #662 (e5de312) into main (0f19c11) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #662      +/-   ##
==========================================
+ Coverage   90.23%   90.26%   +0.03%     
==========================================
  Files         192      192              
  Lines        7238     7262      +24     
  Branches     1153     1153              
==========================================
+ Hits         6531     6555      +24     
  Misses        462      462              
  Partials      245      245              

Impacted Files	Coverage Δ
src/probnum/linops/_linear_operator.py	86.15% <ø> (ø)
...bnum/randprocs/kernels/_exponentiated_quadratic.py	100.00% <ø> (ø)
src/probnum/randprocs/kernels/_kernel.py	92.55% <ø> (ø)
src/probnum/randprocs/kernels/_matern.py	94.11% <ø> (ø)
src/probnum/randprocs/kernels/_polynomial.py	100.00% <ø> (ø)
src/probnum/randprocs/kernels/_product_matern.py	100.00% <ø> (ø)
...c/probnum/randprocs/kernels/_rational_quadratic.py	100.00% <ø> (ø)
src/probnum/randprocs/kernels/_white_noise.py	88.23% <ø> (ø)
src/probnum/_function.py	95.23% <100.00%> (+0.11%)	⬆️
src/probnum/diffeq/_odesolver.py	100.00% <100.00%> (ø)
... and 25 more

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[JonathanWenger]

Note that currently in some classes type hints for Parameters are not shown. This seems to be a bug in automodapi. As this might influence the entire way we currently generate the documentation (i.e. switch to a different plugin for api generation) I would prefer to consider this as out of scope for this PR.

[marvinpfoertner]

Minor stuff, otherwise perfect 👍🏻

[marvinpfoertner]

Just a typo left :)