chore(registry): Update registry helpers to return keyed types

[Bownairo]

Followup from #9772 (comment).

The values returned are derived from RegistrySnapshot, which is a BTreeMap, and so are already unique. The new definitions express this on the type level.

[github-actions]

This pull request changes code owned by the Governance team. Therefore, make sure that
you have considered the following (for Governance-owned code):

1. Update unreleased_changelog.md (if there are behavior changes, even if they are
   non-breaking).

2. Are there BREAKING changes?

3. Is a data migration needed?

4. Security review?

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[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to b0d5e12.

Security Overview

• 🔎 Scanned files: 4 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/f975f1a5-0a47-4a3b-b7f0-a55609e90390?scanId=525b6710-21c8-467d-b45f-cc5fd11a3c4d&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Enhancement	► rs/protobuf/generator/src/lib.rs     Add Ord, PartialOrd derive to hostos_version type attribute ► rs/protobuf/src/gen/registry/registry.hostos_version.v1.rs     Enhance HostosVersionRecord derives to include Ord, PartialOrd and related traits
Refactor	► rs/registry/canister/src/invariants/common.rs     Use BTreeSet in place of Vec for hostos version and API boundary node records; switch insert/collect patterns ► rs/registry/canister/src/invariants/replica_version.rs     Simplify elected versions handling by converting to a BTreeSet from keys

[daniel-wong-dfinity-org-twin]

I updated the title of this PR. PTAL.

The important things that I added:

1. Motivation (avoid linear scan). If you can add more (e.g. some important method is "too" slow), that would be great. Doesn't have to be in the title.

2. Scope: otherwise, "a few" could be anywhere in this large repo.

No canister behavior changes.