Fix display impl for RRuleSet

[fmeringdal]

No description provided.

[tomquist]

Is there anything that's blocking this from being merged?

[fmeringdal]

This is just a partial fix that should fix most use-cases, so I have been hesitant about releasing this "fix" before I get time to fully fix it for all cases.

Have you been running into this bug?

[tomquist]

Yeah, we’re migrating from rrule.js to the rust implementation using a napi wrapper and we’re running into test failures because the string representation didn’t contain all the things an RRuleSet from the JS lib contains.

What is missing in this PR for a full fix?

[fmeringdal]

Cool!

What is missing in this PR for a full fix?

The only thing should be if the rule uses one of the "VALUE=DATE" or "VALUE=PERIOD" properties where it will be interpreted as a date-time rather than just a date or a period.

Maybe you could try to run your test suite against this branch and see if there are other edge-cases not covered as well?