core/generate/utility: rename 'count' field

According to python/mypy#4507, the issue is that `NamedTuple` inherits from
`tuple`, and `tuple` defines a base method `tuple.count`. This causes a problem
for mypy, and currently the best solution is to just pick a different name.

sweetpea/core/generate/sample_non_uniform.py

@@ -35,7 +35,7 @@ def sample_non_uniform_from_specification(spec: ProblemSpecification) -> List[So
           SweetPea's input was given as JSON files. This should no longer be
           necessary.
     """
-    return sample_non_uniform(spec.count, spec.cnf, spec.fresh, spec.support, spec.requests)
+    return sample_non_uniform(spec.sample_count, spec.cnf, spec.fresh, spec.support, spec.requests)
 
 
 def compute_solutions(filename: Path,

sweetpea/core/generate/utility.py

@@ -90,7 +90,7 @@ def from_json(s: str) -> SampleType:
 class ProblemSpecification(NamedTuple):
     """A specification of a complete problem to be solved."""
     sample_type: SampleType
-    count: int
+    sample_count: int
     fresh: int
     support: int
     cnf: CNF
@@ -101,7 +101,7 @@ def from_json(data: JSONDict) -> ProblemSpecification:
         """Converts a JSON object to a ProblemSpecification."""
         return ProblemSpecification(
             sample_type=SampleType.from_json(data['action']),
-            count=data['sampleCount'],
+            sample_count=data['sampleCount'],
             fresh=data['fresh'],
             support=data['support'],
             cnf=CNF(data['cnfs']),