Report signing step to zone status

[tertsdiepraam]

Does a few things:

• Report signing steps to the zone status.
• This required adding a step to the SigningStatus, which kind of overlaps with the current_action but I left that in, because that still shows more granular information that might be helpful for debugging or something.
• There was some info in the status that was shown as "not yet known" even though it was, because the HTTP server only included the signing report on signing review, which is now fixed.
• We now also trigger SigningStatus::InProgress in incremental signing, which turned out to not happen yet.
• We now show the signed serial in the zone status because we now take it from the signing status and not from the signed_review_soa on the storage because the signer knows the serial earlier.
• We now also show the signing strategy (full or incremental).
• Finally, some unused metrics were removed. They were also not created for incremental signing, so this is not a very big deal.

zone:   se
policy: default
source: /home/terts/data/zones/se.zone.stripped.txt

review
  loaded: off
  signed: off

last published
  <no versions published yet>

status: signing
  ✔ load (serial: 1776081352)
  ○ review loaded zone (disabled)
  ● sign (serial: 2026071300)
  |   loaded serial: 1776081352
  |   signed serial: 2026071300
  |   strategy: sign the entire zone
  |   step 1/5: collecting records
  |   start time: 2026-07-13T14:18:15 (9s ago)
  |
  ○ review signed zone (disabled)
  ○ publish

---

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  • Did you run the integration tests with act through the act-wrapper (as described in TESTING.md)?

[ximon18]

I haven't read the changes yet but I like the CLI output updates shown in the PR description!