Unwrap OpaqueRef<T> to T in schema generation and add 'asOpaque: true'

[mathpirate]

Summary by cubic

Unwraps OpaqueRef to its inner type during schema generation and marks schemas with asOpaque: true. This makes derive/lift outputs correctly represent opaque values.

• New Features

  • Unwrap OpaqueRef and add asOpaque: true to the resulting schema.
  • Detect OpaqueRef when it expands to intersection types (OpaqueRefMethods & T).

• Refactors

  • Unified wrapper handling for Cell, Stream, and OpaqueRef; preserves Stream behavior and the Cell<Stream> guard.
  • getNamedTypeKey now treats OpaqueRef as a wrapper to avoid hoisting inner named types.

[ubik2]

looks good. i should make a corresponding change to JSONSchema
Edit: #1854