[horhulenko]

Every simplify() call made a copy of ABC's result in translate_from_abc() and never deleted it, about 376 KB each time. A few small strings went the same way. Now they are freed, like ABC's own Verilog writer does.

The mutex in abc_simplification() is now a std::lock_guard, because one failed simplification used to keep it locked and freeze the next one.

Memory leaked, measured with LeakSanitizer

	before	after
1000 simplify() calls from Python	376MB	0
runTest-boolean_function	22MB	0
runTest-solve_fsm	14MB	0

This touches the same lines as #677, so whichever lands second needs a small rebase.

[joern274]

Good work!