projects: add github.com/tmm1/taxes.cue

[mvdan]

@tmm1's project has uncovered at least three potential regressions in v0.5.0-beta.5:

• evaluator: regression when comparing incomplete structs to bottom cue-lang/cue#2245
• evaluator: repeated use of embedded disjunction results in "field not allowed" cue-lang/cue#2246
• cmd/cue: serious performance regression cue-lang/cue#2243

His code is open source, and his make test is a good command we can run in Unity to verify that it hasn't been broken - note that all it really does is cue export test.cue.

We'll have to make the test run reasonably quickly and give the expected output again - then we can add the project to Unity.

[mvdan]

Now added; we're still blocked by 2243 to run the entire test suite in a matter of seconds, but that thread is already tracking the performance issue to be fixed.