Clarify set_adapters() adapter_weights documentation and type hints #15146

Follow-up to #15128.

During the review of #15128, @BenjaminBossan suggested improving the adapter_weights docstring and type annotation in LoraBaseMixin.set_adapters(), and @sayakpaul agreed. The PR was merged before I could include these changes. On current main, the docstring still describes adapter_weights as list[float, float], but the method also accepts scalars, dictionaries, lists of weights, and None. The type annotation also uses dict without specifying the key and value types.

A small follow-up could:

• Explain the supported weight formats and how the same component-weight dictionary is used for multiple adapters.
• Explain per-adapter and nested component weights where supported.
• Make the type annotation more specific without changing how the method works.

I already wrote and tested these changes while working on #15128. Would a small follow-up PR for these changes be appropriate?