[svsim] Fix deadlock in long simulations by flushing expectation queue

[Emin017]

This patch fixes a deadlock issue that occurs during long-running simulations where a large number of peek/poke/expect operations are performed.

Ref: #5128 and #5129

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Type of Improvement

• Bugfix

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Release Notes

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[seldridge]

Thanks for this!

This is definitely an improvement. This also made me realize what I think the problem is... The issue is that if the command buffer gets too big, the C++ side will block once stdin fills. The real fix here is to have the C++ side not block waiting for the entire buffer, I think.

I do think that there is sill a failure mode here where a user does enough pokes to fill the buffer without a single expect/tick.

A few comments throughout. However, I'm good with this generally