Improve CQ1

[iamcarbon]

This PR.

• Eliminates a few list allocations (and possible internal resizes) by using arrays
• Eliminates a queue allocation
• Ensures string comparisons are invariant
• Eliminates a possible NRE when allocating ReferralLinksExtension with a null value and subsequently adding additional rels

[MihaZupan]

There's some overlap with #527 on the Rel changes.

I don't think we'd want to bump the target just for this. We did already but reverted that, see #466.

[iamcarbon]

@MihaZupan -- It looks like you won the race to fix these nullable violations.

Let's get your change committed first and I'll rebase and start a new PR with a clean history.