Fix pyright errors in arcade.gl

[cspotcode]

Followup to #1751. Will need a rebase after #1751 gets squashed. Requesting a review from @einarf , but no rush, I know you're slowly getting back into things.

[cspotcode]

@gran4 Thanks for taking a look, but unfortunately, this PR can't be reviewed yet. It's stacked on top of #1751 so the diff is all wonky. It'll be reviewable once #1751 merges.

[gran4]

Oh, ok you should make it a draft then. (unless there is something I don't understand)

[einarf]

The gl stuff looks perfectly reasonable 👍

[cspotcode]

@einarf Thanks for taking a look! I marked this PR as draft while we wait for #1751 to merge. Once #1751 is merged, I'll rebase this PR, bring it out of draft, and ping you for a merge.

[cspotcode]

I rebased yesterday, but there are still one or two mypy errors I need to understand and fix before this can merge. I'll solicit a review after I've fixed them.

[cspotcode]

@einarf I need some help understanding some of the gl types.

arcade/arcade/gl/vertex_array.py

Lines 195 to 196 in 889772d

	f"Program attribute '{prog_attr.name}' has type {gl_name(prog_attr.gl_type)} "
	f"while the buffer description has type {gl_name(attr_descr.gl_type)}. "

I get a typecheck diagnostic Argument 1 to "gl_name" has incompatible type "Optional[int]"; expected "int"
This is because prog_attr.gl_type is Optional[int]

Is that correct, should AttribFormat.gl_type be Optional?

AttribFormat is instantiated here:

arcade/arcade/gl/program.py

Lines 394 to 401 in 889772d

	AttribFormat(
	c_name.value.decode(),
	type_info.gl_type,
	type_info.components,
	type_info.gl_size,
	location=location,
	)
	)

and here:

arcade/arcade/gl/types.py

Lines 311 to 314 in 889772d

	AttribFormat(
	attr_name, gl_type, components, byte_size, offset=self.stride
	)
	)

For the latter, gl_type is possibly None because it comes from _formats, which has some None values in x1, x2, x4, x8

arcade/arcade/gl/types.py

Lines 196 to 220 in 889772d

	_formats: dict[str, tuple[Optional[PyGLenum], int]] = {
	# (gl enum, byte size)
	# Floats
	"f": (gl.GL_FLOAT, 4),
	"f1": (gl.GL_UNSIGNED_BYTE, 1),
	"f2": (gl.GL_HALF_FLOAT, 2),
	"f4": (gl.GL_FLOAT, 4),
	"f8": (gl.GL_DOUBLE, 8),
	# Unsigned integers
	"u": (gl.GL_FLOAT, 4),
	"u1": (gl.GL_FLOAT, 1),
	"u2": (gl.GL_FLOAT, 2),
	"u4": (gl.GL_FLOAT, 4),
	# Signed integers
	"i": (gl.GL_INT, 4),
	"i1": (gl.GL_BYTE, 1),
	"i2": (gl.GL_SHORT, 2),
	"i4": (gl.GL_INT, 4),
	# Padding (1, 2, 4, 8 bytes)
	"x1": (None, 1),
	"x2": (None, 2),
	"x4": (None, 4),
	"x8": (None, 8),
	}