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Describe the bug
For some reason, CNR provider will try to update duplicated NS record if NAMESERVER is set even.
Here is the dnscontrol preview output

******************** Domain: mydomain.net
1 correction (CNR)
#1: Update nameservers ns1.domain-dns.com,ns2.domain-dns.net-> ns1.domain-dns.com,ns1.domain-dns.com,ns2.domain-dns.net,ns2.domain-dns.net
Done. 1 corrections.

As you can see based on the above output, CNR trying to update match NAMESERVER record by duplicate each one twice.

To Reproduce
Steps to reproduce the behavior:

1. Simple DNS config file as following

var REG_CNR = NewRegistrar("CNR");
var DSP_CF = NewDnsProvider("cloudflare");

D("mydomain.net", REG_CNR,
  DnsProvider(DSP_CF),
  DefaultTTL(3600),

  NAMESERVER("ns1.domain-dns.com")
  NAMESERVER("ns2.domain-dns.net")

  MX(".....")
  (rest of other records, A, TXT etc)
};

3. Try to run dnscontrol preview
4. See error (I didn't try to push the change yet so I don't know what ends result will be)

Expected behavior

• Won't update if it's same (in my case)
• OR, update it only once if it changed. (but looks like it trying to update twice)

REG Provider

• CNR

DNS Provider

• Cloudflare (but shouldn't matter)

Additional context
dnscontrol version: v4.30.0
go version: 1.25.1
OS version: Debian 12