feat(DeriveArbitrary): Support structure-parameterized types

[mwhicks1]

Extend the Arbitrary deriving handler to support inductive types parameterized by structures. For structure parameters, recursively expand Type-valued fields into per-field inst-implicit binders (e.g., [Arbitrary T.Meta] or [Arbitrary T.base.IDMeta] for nested structures).

Add mkArbitraryInstBinders which replaces mkInstImplicitBinders in mkHeaderWithOnlyImplicitBinders and mkArbitraryFueledInstanceCmds. For each parameter:

• If [Arbitrary param] is type-correct, emit it (existing behavior)
• Otherwise, if the param's type is a structure, recursively expand its fields, emitting [Arbitrary proj] for each Type-valued leaf
• Reject structures with non-Type, non-structure fields (effectively indexed types) with a clear error message

Add StructureParameterTest.lean covering:

• Simple structure parameters
• Mixed normal type + structure parameters
• Nested structure parameters (structure containing structure)
• Rejection of structures with non-Type fields