.add_sync_process() is deprecated

[lonjil]

The simulations use .add_sync_process(), which emits a deprecation warning.

I am very new to Amaranth, so I may be missing something, but .add_process() appears to work just fine.

[bl0x]

Amaranth HDL completely changed the way simulations work (going to async functions instead of synchronous). I'll now migrate the code to use the new system step by step. Since these simulations are testbenches, I'll use .add_testbench(). Also take a look here for reference: https://amaranth-lang.org/docs/amaranth/latest/simulator.html