feat: Post Python 3.10 bump, where relevant, use KW_ONLY sentinel values

[daniel-dodd]

Feature Request

Post Python 3.10 bump #370, to avoid issues with default values, we should use the KW_ONLY, e.g., for names most notably this would be great for default kernel stuff like the computations, active_dims, that get in the way!

@dataclass
class AbstractKernel(Module):
    r"""Base kernel class."""
    _: KW_ONLY # <-------------- INTRODUCE HERE:
    compute_engine: AbstractKernelComputation = static_field(DenseKernelComputation())
    active_dims: Optional[List[int]] = static_field(None)
    name: str = static_field("AbstractKernel")