TDML runner needs to support pre-compiled DFDL schema

On a large schema project, we're unable to use TDML-based tests at all, because compiling the schema takes much too long. 

Even though the TDML runner caches these, it still compiles at least once for every time you invoke a test suite or a single test. 

That takes 1 to 2 minutes for this large schema. 

We need an option to tell a TDML test that the "model" is a pre-compiled DFDL schema file.