fix(civo): normalize @ apex record names

[linusfr]

What does it do ?

Normalizes Civo's "@" apex marker to ExternalDNS's empty-name convention for A and AAAA records. This lets apex records resolve and match as example.com instead of @.example.com.

Motivation

Civo returns "@" for apex address records. Without normalization, reconciliation cannot match existing apex records and repeatedly attempts to recreate them.

This reopens the stale #6184 from @cjohnhanson. It incorporates @ivankatliarchuk's feedback: normalization is extracted into a helper and restricted to A/AAAA records. Create/update responses are not used; matching occurs against listed records before changes are submitted.

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

Verified: go test -race ./provider/civo passes.

[kubernetes-prow]

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• ✅ login: linusfr / name: Linus Frotscher (e79858c)

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[kubernetes-prow]

Hi @linusfr. Thanks for your PR.

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[linusfr]

@ivankatliarchuk This refreshes #6184 with requested helper extraction and A/AAAA-only normalization. go test -race ./provider/civo passes. Could you please review and, if appropriate, run /ok-to-test?
Thank you.