Fixes yield proc scheduling. Turns sleeps into an opcode

[Cyberboss]

The behavior is now the same for either spawn or sleep:

• delay < 0: Proc will continue immediately if nothing is scheduled in the same tick. Otherwise, same as delay == 0.
• delay == 0: Proc scheduled on end of same tick.
• delay > 0: Proc scheduled after n ticks.

This also fixes the ProcScheduler being able to still have queued procs when running multiple tests in serial.

Then, to fix perf issues I had to redo sleeping into an opcode:

• Remove sleep from DMStandard.
• Two new opcodes Sleep and BackgroundSleep (which is just sleep -1, much faster than popping a float off for background sleeps).
• Create new lightweight async proc state for sleeping.
• Compiler/runtime adjustments to handle new opcodes.
• Added IOpenDreamGameTiming as a wrapper around IGameTiming that we can control in unit tests.

Closes #1262