Possibly restore/continue the simulator rework

[YuriSizov]

With commit 2c414eb I removed every file and line of code related to simulators (/sequencer/simulator).

This code was entirely unused. It seems to be a part of a larger refactoring in the original SiON which started 12 years ago, but was never finished. As it stands, having dead code like that is not useful, and the internal nature of this particular code means it's not useful to external users either.

So it's gone from the main branch now. But, should we ever need it, the latest commit to include it is marked as a wip-simulator branch.