Standing TXT record at _validation-persist.<domain> eliminates per-renewal
DNS updates. Auto-fallback to dns-01 if CA doesn't offer dns-persist-01.
ScriptDNSSolver extended with PresentPersist method. Configurable via
CERTCTL_ACME_CHALLENGE_TYPE=dns-persist-01 and
CERTCTL_ACME_DNS_PERSIST_ISSUER_DOMAIN env vars.
Also fixes IsExpired edge-case test in discovery_test.go that always failed
due to time.Now() drift between test setup and method invocation.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Remove unused repository import from discovery_handler_test.go and
unused tests variable from discovery_test.go (replaced by testCases).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>