Improve tests and allow BigInts on `findByPk`

[papb]

Hello! :smiley:

This PR does several things:

• Refactors some tests using async/await instead of promises (and other readability improvements)
• Fixes some tests that weren't waiting for promises correctly and passing without really testing anything (example)
• Adds a thorough cleanup step after each test to avoid interference between tests - this also allowed me to unskip an entire describe suite
• Adds a "basic usage" test in which basic Sequelize things are used - I suggest using this test to back the claim of "alpha support" :tada:
  • When I added this test, it failed, but the solution was simple (just allow BigInts on findByPk), so I did it myself! :tada:
• Enables skipping the huge & slow sequelize integration tests by writing the following in the end of the commit message:

  [[skip sequelize integration tests]]

• Converts the see-upsert-working.js file (that I created in #47) into a real test

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You can see the new [[skip sequelize integration tests]] feature working at my fork (once this PR is merged, it will start being applied on this repo automatically) - it only has 2 checks instead of over 200. This is great for faster feedback and for saving energy, for situations in which we don't really want to see all those checks (which is exactly the case for this PR, since I didn't change anything that I expect to make a difference on those results).

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Suggestion: I think an admin of this repository should set the two "main" checks as required for merges (at some point, perhaps not now while many changes are still being done):

• Main - CRDB v20.2.4, Sequelize v5
• Main - CRDB v20.2.4, Sequelize v6

This can be done in the Require status checks to pass before merging section, here:

[vy-ton]

@RichardJCai Pedro (@papb) was the Sequelize maintainer we were first working with. This is his final PR with some improvements that he shared. Can you help merge this work with the ongoing work from our other contractors?

[RichardJCai]

@RichardJCai Pedro (@papb) was the Sequelize maintainer we were first working with. This is his final PR with some improvements that he shared. Can you help merge this work with the ongoing work from our other contractors?

Ack, will do.

[RichardJCai]

LGTM thanks!