Overloaded type annotations not compiled by Sphinx

### What's the problem?

We have used the `overload` decorator to provide more specific type hints in several places, e.g. in `kernels.ScalarValuedKernel`, but these are not rendered by Sphinx. Instead, Sphinx just shows the generic `Union` of several possible types. Moreover, if we rely on `overload` with class inheritance, no annotations are compiled at all, e.g. `kernels.scalar_valued.SquaredExponentialKernel.compute_elementwise`.

`overload` with class inheritance should work as of Python 3.12 - I'm unsure about earlier Python versions. Sphinx issues from a few years ago (pre-Python 3.12) also suggest this should work.

### How can we reproduce the issue?

Compile documentation and look at classes mentioned above.

### Python version

3.12

### Package version

0.2.1

### Operating system

Windows

### Other packages

_No response_

### Relevant log output

_No response_