fix(transfer): accept external nameservers without registry validation (#525)

[msiouti]

Fixes #525.

Problem

APITools::createNameserversArray gated nameserver inclusion on the ability to resolve an IP for every NS — first via Openprovider's searchNsRequest registry lookup, then via gethostbyname. For out-of-bailiwick nameservers (the vast majority of real-world cases — ns1.cloudflare.com, dns.google, etc.) neither path is appropriate: the registry lookup is for glue records only, and gethostbyname can fail or return the input unchanged. When that happened the NS was silently dropped from the array, the truncated list was passed to transferDomainRequest, and the registry substituted the reseller's default nameservers — silently changing customer DNS delegation at the moment of transfer, with no exception or warning.

Fix

Scope IP resolution to in-bailiwick glue records only — i.e. NS that are the apex domain itself or a subdomain of the domain being registered/transferred. Out-of-bailiwick NS are now accepted by name alone and serialized without an ip field. Glue records still try the registry first, then DNS resolution; if neither produces a valid IPv4 the function throws with a clear message instead of dropping the NS.

The two code paths in the original (test_mode == 'on' and the default branch) collapsed into one because their differences were incidental to the fix and the new path is a strict superset.

Changes

• OpenProvider/API/APITools.php — createNameserversArray rewritten; two new private helpers isGlueRecord and resolveGlueIp extracted.
• tests/API/APIToolsTest.php — new PHPUnit cases:
  • test_external_nameservers_are_accepted_without_ip_lookup — the direct regression test for [BUG] transferDomain silently replaces external nameservers with module defaults — APITools::createNameserversArray regression #525; asserts apiHelper::getNameserverList is not called for non-glue NS.
  • test_explicit_ip_in_name_slash_ip_form_is_preserved
  • test_glue_record_without_resolvable_ip_throws
  • test_glue_record_uses_registry_ip_when_available
  • test_throws_when_fewer_than_two_nameservers_supplied
  • test_mixed_glue_and_external_nameservers
  • test_nameserver_names_are_lowercased

Risk / verification

• DomainNameServer::$ip already defaults to null, so omitting the key from the constructor array leaves the property null. The Symfony PropertyNormalizer used by ApiHelper will emit ip: null for external NS in the request body. If, in review, we'd rather suppress the null entirely, the smallest follow-up is to make DomainNameServer implement JsonSerializable and skip null fields — happy to add that in this PR if reviewers prefer.
• All three callers (DomainController::transfer, DomainController::register, NameserverController::saveNameservers) use the return value as-is — no caller-side changes required.
• PHP floor in composer.json resolves to >= 8.1 (per vendor/composer/platform_check.php), so str_ends_with is available natively.

Test plan

• CI passes (PHPUnit + lint).
• Manual: transfer a domain with external NS (e.g. Cloudflare) and confirm the registry receives those NS — not the reseller defaults.
• Manual: transfer a domain using glue NS (ns1.<being-transferred>.tld) with explicit name/ip and confirm IP is preserved.
• Manual: attempt transfer with glue NS missing IP and unresolvable hostname; confirm a clear error surfaces in WHMCS instead of a silent default-substitution.