Fix CDS/CDNSKEY RRsets comparison in DNSSEC15

[tgreenx]

Purpose

This PR proposes a fix to the handling of CDS and CDNSKEY RRsets comparison in DNSSEC15.

PS: The proper fix for the code below https://github.com/zonemaster/zonemaster-engine/pull/1383/files#diff-3c6ad87ddb974fb813839bacdaafd4e212c238d0ff6865a9bf6cf677403343deR3953 requires changes in LDNS. PRs have been made to make it happen, and it should be available in the next release of LDNS (1.8.5). See NLnetLabs/ldns@b398138.

Context

Fixes #1381

Requires zonemaster/zonemaster-ldns#199

Changes

• Update code logic
• Refactoring

How to test this PR

This requires zonemaster/zonemaster-ldns#199.

Unit tests should pass.

Manual testing (from #1381):

$ zonemaster-cli 8.1.7.0.1.0.0.2.ip6.arpa --ns decsys.vsb.cz --ns nsa.ces.net --ns nsa.cesnet.cz --show-testcase --test dnssec15
  -
Seconds Level    Testcase       Message
======= ======== ============== =======
Looks OK.

[tgreenx]

PS2: A more elegant solution to this PR would require more change in Zonemaster-LDNS. See zonemaster/zonemaster-ldns#196.

I've proposed zonemaster/zonemaster-ldns#203, which would allow for making a more straightforward solution for this PR. So I'm switching it to a draft state for now.

[tgreenx]

I've proposed zonemaster/zonemaster-ldns#203, which would allow for making a more straightforward solution for this PR. So I'm switching it to a draft state for now.

@mattias-p @matsduf @MichaelTimbert @marc-vanderwal This PR has been updated and is now ready for review.

[matsduf]

I find the code quite hard to follow. I would like to see comments that says what sections are meant to do. This is not due to the current PR. That is how the code is already. But that fact makes it harder to review the code.

I have tested the update and I have found no issues.

[matsduf]

@mattias-p , @marc-vanderwal, @MichaelTimbert - please review.

[marc-vanderwal]

I suggest that we wait until zonemaster/zonemaster-ldns#209 is merged.

[tgreenx]

@matsduf please re-review

[matsduf]

Reviewed for release testing of v2024.2: no issues.