Diagnostic results are inconsistent when using "--threads" option on sympy

The "mypy_primer" results for sympy consistent show differences between runs. This is likely due to circular dependencies within the sympy code, but an investigation should verify this hypothesis. If possible, it would be preferable to improve the repeatability even when type checking is parallelized using "--threads".

Start by running mypy_primer against sympy repeatedly with the --threads option and compare the diagnostic results between runs. Investigate whether circular dependencies explain the differences; done means either improving repeatability for parallel type checking or documenting the verified cause and limitations.

Written by the indexing model from the issue text.