`'arguments-v3'` schema improvements

[Viicos]

Following #1641, some improvements that could be implemented:

• deduplicate name and lookup_key_collection (comment):
  

  pydantic-core/src/validators/arguments_v3.rs

  Lines 49 to 52 in b6a2ca1

  	struct Parameter {
  	name: String,
  	mode: ParameterMode,
  	lookup_key_collection: LookupKeyCollection,

• Extract potential var_args/var_kwargs parameter (comment):

  positional_args: Vec<Parameter>,
  var_args: Option<Parameter>,
  keyword_only_args: Vec<Parameter>,
  var_kwargs: Option<Parameter>,

• Extra behavior for extra args, when input is ArgsKwargs. Currently, this is relevant for kwargs (on both schema types), but not for args (comment).