Add integration tests for 'Synthesize Sequences' demo

[npatki]

Problem Description

As part of migrating to SDV 1.0, we are creating new demos! Since running the old demos as a workflow caused problems (took a long time and sometimes failed due to jupyter dependencies), we want to make sure that all of the processes in the new demos are made into integration tests.

Expected behavior

• Make integration tests for all of the SDV processes ran in the "Synthesize Sequences" demo.

Technical Details

• Put the tests in the appropriate files
• We don't need to be very strict on the asserts. Just add basic asserts to ensure things aren't broken. For example,
  • Assert sampled data is the right shape
  • Validate the sampled data
  • Make sure any key values in the output are present