feat: support sqlite window functions

[machow]

This PR does the following:

• implements window functions (which sqlite started supporting a few years ago)
  • includes dply vector functions. E.g. dense_rank()
• implements some aggs which I thought sqlite didn't support (e.g. n())
• remove most cases of skipping sqlite from unit tests!
• fixes failing bigquery tests (that were accidentally skipped on CI)