Use strings for closed SOAP anyURI value locals

Replace method-local SoapAnyUri constructor/Parse wrappers with string locals only when every reference is an attributed read of Value. Framework SoapAnyUri stores strings without validating or normalizing URIs. Keep evaluation at the declaration, null values, and canonical local symbols. Escapes, writes, captures, nameof, multiple declarators, conditional-compilation files and scoped/global remoting imports remain for review.