Re-use host Python process when compiling from command line

[ducky64]

... instead of spawning a sub-process. This keeps namespaces consistent (in a way that spawning a subprocess wouldn't) and allows the use of a Python debugger. Resolves #362

NOTE FOR DEBUGGING: the IDE (compile-design) does not yet support debugging, so you'll need to create a main stub (like bllinky_skeleton.py, as if running from the command line) and debug from that. But breakpoints do work.

Implementation-wise, this 'flips' the client / server role: after sending the design to compile to the server, the Python process then acts as an HDL server until receiving an empty request (denoting end of compilation), then waits for the compilation result. This also restructures the interface structure, notably bringing the core compiler interface structurally closer to the Python implementation, with a dedicated serializer / deserializer class (instead of it being monolithic).

This also refactors the compiler to eliminate error suppression, instead moving it into the generator test case (using redirect_stderr) which is the only place this functionality is used. This new structure also un-suppresses a warning in the test suite, which will be addressed separately.

Also bumps the compiler version.