Implement the rest of CEL

[Flaque]

Overview

This PR adds support for the rest of CEL.

We @ sfcompute.com are interested in using CEL for ourselves, but would like a reasonable typescript implementation to exist.

So this PR hooks up the conformance tests from the CEL spec into a test framework, and then iteratively makes all of them pass.

It adds functionally every missing feature and resolves a lot of the edge cases from the existing implementation.

Apologies for the large PR!

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [x] I have added tests (if possible)
• [x] I have updated the readme (if necessary)
• [x] I have updated the demo (if necessary)