[docs] Fix docstring arguments that don't match the signatures

[revanth-045]

What does this PR do?

Four public docstrings describe parameters the functions don't accept (or a return type they don't produce), so the rendered API docs mislead callers:

Function	Docstring says	Signature has
TransformerSpatioTemporalModel.forward	num_frames (int)	(not a parameter — frames are inferred from image_only_indicator)
get_2d_rotary_pos_embed_lumina	grid (np.ndarray)	len_h, len_w (now documented)
AutoencoderKLHunyuanImageRefiner.tiled_decode	return_dict; returns DecoderOutput or tuple	(no return_dict; returns torch.Tensor)
AutoencoderKLHunyuanVideo15.tiled_decode	return_dict; returns DecoderOutput or tuple	(no return_dict; returns torch.Tensor)

Docstring-only; no behaviour changes. None of the touched blocks are # Copied from targets. ruff check, ruff format --check, and doc-builder style --check_only pass on the changed files.

Before submitting

• Did you read the contributor guideline?
• Did you write any new necessary tests? (docs only)

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[github-actions]

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