feat: add constructors for VectorObject2D and MomentumObject2D

[henryiii]

Closes #88.

WIP, currently just 2D Object implemented.

[codecov-commenter]

Codecov Report

Base: 81.04% // Head: 81.08% // Increases project coverage by +0.03% 🎉

Coverage data is based on head (d9a4462) compared to base (23a10c5).
Patch coverage: 78.87% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #89      +/-   ##
==========================================
+ Coverage   81.04%   81.08%   +0.03%     
==========================================
  Files          96       96              
  Lines       10624    10672      +48     
==========================================
+ Hits         8610     8653      +43     
- Misses       2014     2019       +5     

Impacted Files	Coverage Δ
src/vector/backends/numpy.py	78.10% <ø> (ø)
src/vector/backends/awkward.py	51.63% <33.33%> (ø)
src/vector/_methods.py	78.60% <70.96%> (-0.10%)	⬇️
src/vector/backends/object.py	73.67% <94.11%> (+0.50%)	⬆️

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[Saransh-cpp]

I went through the overloads of vector.obj and a user can indeed create a MomentumObject by specifying a mixture of momentum and generic coordinates. I think this should be removed and the momentum coordinate names must be converted to generic in the __init__ method of VectorObject classes, which will then be inherited by MomentumObject classes.

[Saransh-cpp]

Removing the MomentumObject constructor and changing the momentum coordinates to generic ones works!

Suggested change

	def __init__(
	self, azimuthal: typing.Optional[AzimuthalObject] = None, **kwargs: float
	) -> None:
	if not kwargs and azimuthal is not None:
	self.azimuthal = azimuthal
	elif kwargs and azimuthal is None:
	if set(kwargs) == {"x", "y"}:
	self.azimuthal = AzimuthalObjectXY(kwargs["x"], kwargs["y"])
	elif set(kwargs) == {"rho", "phi"}:
	self.azimuthal = AzimuthalObjectRhoPhi(kwargs["rho"], kwargs["phi"])
	else:
	raise TypeError("invalid arguments, must be x=, y= or rho=, phi=")
	else:
	raise TypeError("must give Azimuthal if not giving keyword arguments")
	def __init__(
	self, azimuthal: typing.Optional[AzimuthalObject] = None, **kwargs: float
	) -> None:
	for k, v in kwargs.copy().items():
	kwargs.pop(k)
	kwargs[_repr_momentum_to_generic.get(k, k)] = v
	if not kwargs and azimuthal is not None:
	self.azimuthal = azimuthal
	elif kwargs and azimuthal is None:
	if set(kwargs) == {"x", "y"}:
	self.azimuthal = AzimuthalObjectXY(kwargs["x"], kwargs["y"])
	elif set(kwargs) == {"rho", "phi"}:
	self.azimuthal = AzimuthalObjectRhoPhi(kwargs["rho"], kwargs["phi"])
	else:
	raise TypeError("invalid arguments, must be x=, y= or rho=, phi=")
	else:
	raise TypeError("must give Azimuthal if not giving keyword arguments")

[Saransh-cpp]

A minor issue with this -

vector.obj(rho=1, phi=2)

right now constructs a VectorObject2D object.

But the user would now also be able to do -

vector.MomentumObject2D(rho=1, phi=2)

[Saransh-cpp]

I think this PR should work now, given that we are fine with passing generic coordinates into MomentumObject classes. The same is under discussion for the shortcut constructors (obj here), which can be handled in another PR.

[henryiii]

Feel free to turn of the unreachable check for mypy if it triggers too much, and 1-2 type ignores need [misc] added.

[Saransh-cpp]

Done! I've also refactored out the type safety code from the obj constructor.

[henryiii]

I can't approve "my own" (according to GitHub) PR, but I reviewed it so verbally approving here!

[Saransh-cpp]

Merged! Thanks for the review! 🎉