Preserve Framework SOAP duration formatting

Replace attributed SoapDuration.ToString(TimeSpan) calls with a private formatter retaining Framework's 360-day years, 30-day months, fixed fields, seven-digit nonzero fractions, and negative sign for zero. Evaluate the duration once and support TimeSpan.MinValue. Parsing, partial/struct containers, lambdas/query expressions, conditional files and scoped/global imports remain for review; this does not substitute XmlConvert's different wire format.