fix: upsert_record(condition_expression=)

[fwereade]

Notes

• (Narrowly) addresses the bug observed in Example for conditional upsert #70
  • doesn't attempt to convert the boto ClientError on condition reject
• The only actual change is in DynamoTable.upsert_record, everything else is remedial:
  • Fixes tests broken since Pass through consistent read flags for batch gets, and queries. #80
  • Fixes from black, isort, mypy

I feel like rolling a version update into this PR would be a bridge too far, but – assuming this fix is viable – it'd be most useful if it could go into a release fairly soon (see #83 )

Public API changes

Changed

The condition_expression parameter to DynamoTable.upsert_record now takes values from extra_data to compose a ConditionExpression for the API call.