opengl: deprecate unused dim parameter on OpenGLMobject

## Source

Two related sites in `manim/mobject/opengl/opengl_mobject.py`
(as of HEAD ):

Line 156 — the parameter declaration in `OpenGLMobject.__init__`:

```
def __init__(
self,
color: ParsableManimColor | Sequence[ParsableManimColor] = WHITE,
opacity: float = 1,
dim: int = 3, # TODO, get rid of this
...
```

Line 185 — the instance attribute assignment:

`self.dim: int = dim # TODO, get rid of this`

## Problem

The `dim` parameter on `OpenGLMobject.__init__` is paired with two in-source TODOs asking for its removal. The parameter is declared with a default of `3`, stored as `self.dim`, and does not appear to be consulted anywhere in the constructor or in obvious downstream code paths. It looks like a vestigial parameter from an earlier version of the class.

Because `dim` is a public constructor parameter, code outside the project may pass it explicitly. Direct removal would be a breaking change.

## Suggested approaches

- Audit all references to `dim` and `self.dim` across the codebase (including subclasses of `OpenGLMobject`) to confirm the parameter is genuinely unused.
- Deprecate the parameter with a `DeprecationWarning` when callers pass it explicitly, suggesting they stop doing so.
- After a deprecation period, remove the parameter and the attribute.
- Apply the same treatment to any subclass `__init__` that forwards `dim` to `super().__init__()`.

Start in manim/mobject/opengl/opengl_mobject.py at OpenGLMobject.__init__ lines 156 and 185. Audit all references to dim and self.dim across the codebase, including subclasses that forward dim to super().__init__(). Done means the unused public parameter has a documented deprecation path, explicit callers receive the intended warning, and affected subclasses are covered.

Written by the indexing model from the issue text.