🔧 MAINTAIN: Improve type annotations of @classproperty

[chrisjsewell]

Taken from python/mypy#2266 (comment).

These annotations allow for static analysis to correctly return the correct type.

As an example:

example.py

from typing import Any, Callable, Generic, TypeVar

ReturnType = TypeVar('ReturnType')

class classproperty(Generic[ReturnType]):

    def __init__(self, getter: Callable[[Any], ReturnType]) -> None:
        self.getter = getter

    def __get__(self, instance: Any, owner: Any) -> ReturnType:
        return self.getter(owner)

class Example:

    @classproperty
    def class_property(cls) -> str:
        return 'class property'

reveal_type(Example.class_property)

$ mypy example.py
note: Revealed type is "builtins.str*"

as opposed to without annotations:

$ mypy example.py
note: Revealed type is "Any"

You can also get the correct type when using VS Code's Pylance, although pytest still seems to have problems with it (pylint-dev/pylint#1694 (comment)).

[codecov]

Codecov Report

Merging #5176 (b657831) into develop (ddad09c) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #5176      +/-   ##
===========================================
+ Coverage    80.90%   80.93%   +0.04%     
===========================================
  Files          536      536              
  Lines        37054    37056       +2     
===========================================
+ Hits         29975    29988      +13     
+ Misses        7079     7068      -11     

Flag	Coverage Δ
django	75.79% <100.00%> (+0.04%)	⬆️
sqlalchemy	74.93% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiida/common/lang.py	80.00% <100.00%> (+1.06%)	⬆️
aiida/orm/nodes/process/calculation/calcjob.py	78.00% <0.00%> (+0.96%)	⬆️
aiida/engine/processes/calcjobs/tasks.py	65.78% <0.00%> (+1.01%)	⬆️
aiida/engine/daemon/client.py	76.27% <0.00%> (+1.02%)	⬆️
aiida/engine/processes/calcjobs/manager.py	86.73% <0.00%> (+3.54%)	⬆️

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