Fix Lark LaTeX derivative fraction parsing - #30503

#### References to other Issues or PRs

Fixes part of #30486.

#### Brief description of what is fixed or changed

The Lark LaTeX parser returned a raw tuple for derivative fractions such as `\frac{dy}{dx}`. This changes the transformer to return a SymPy `Derivative(y, x)` instead.

Added regression tests for `\frac{dy}{dx}` and `\frac{d y}{d x}`.

#### Other comments

Tested with:

```bash
python -m pytest sympy/parsing/tests/test_latex_lark.py -k differential_fraction_derivative
```
Result: `1 passed`.

#### Release Notes
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