Fixes # .

Summary/Motivation:

This PR attempts to resolve two intermittent test failures:

• On OSX (usually Python 3.10), we occasionally get a solver test failing with "I/O operation on a closed file". This PR removes the flush() that can trigger this error. The streams that were being flushed are already being flushed just before reaching this code (rendering this call redundant).
• On PyPy, we see a test failure caused by what looks like an incomplete GC run. This adds short delays between calls to the GC to hopefully resolve the problem.

Changes proposed in this PR:

• See above

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