[posix] update Posix::Resolver to support IPv6 addresses for servers.

[yangsong-cnyn]

• This change is needed to support RDNSS, as requested in [dns] OTBR not correctly parsing the RDNSS Option in RA message? ot-br-posix#2685.

This PR enhances the DNS resolver (resolver.cpp) to support IPv6 addresses in upstream DNS server configurations, allowing for greater flexibility and compatibility in IPv6-enabled environments.

Key Changes:

• IPv6 Parsing in LoadDnsServerListFromConf:
  • The LoadDnsServerListFromConf function now parses both IPv4 and IPv6 addresses from /etc/resolv.conf using inet_pton with AF_INET and AF_INET6.
  • Parsed addresses are stored in mUpstreamDnsServerList.
• IPv6 Handling in Query:

[size-report]

Size Report of OpenThread

Merging #11325 into main(4c0af02).

name	branch	text	data	bss	total
ot-cli-ftd	main	474840	860	66364	542064
	#11325	474840	860	66364	542064
	+/-	0	0	0	0
ot-ncp-ftd	main	442844	764	61584	505192
	#11325	442844	764	61584	505192
	+/-	0	0	0	0
libopenthread-ftd.a	main	242440	95	40142	282677
	#11325	242440	95	40142	282677
	+/-	0	0	0	0
libopenthread-cli-ftd.a	main	59395	0	8083	67478
	#11325	59395	0	8083	67478
	+/-	0	0	0	0
libopenthread-ncp-ftd.a	main	32911	0	5924	38835
	#11325	32911	0	5924	38835
	+/-	0	0	0	0
ot-cli-mtd	main	368840	764	50844	420448
	#11325	368840	764	50844	420448
	+/-	0	0	0	0
ot-ncp-mtd	main	351324	764	46088	398176
	#11325	351324	764	46088	398176
	+/-	0	0	0	0
libopenthread-mtd.a	main	161313	0	24646	185959
	#11325	161313	0	24646	185959
	+/-	0	0	0	0
libopenthread-cli-mtd.a	main	40296	0	8059	48355
	#11325	40296	0	8059	48355
	+/-	0	0	0	0
libopenthread-ncp-mtd.a	main	25561	0	5924	31485
	#11325	25561	0	5924	31485
	+/-	0	0	0	0
ot-cli-ftd-br	main	562688	868	133300	696856
	#11325	562688	868	133300	696856
	+/-	0	0	0	0
libopenthread-ftd-br.a	main	335647	100	107046	442793
	#11325	335647	100	107046	442793
	+/-	0	0	0	0
libopenthread-cli-ftd-br.a	main	73857	0	8115	81972
	#11325	73857	0	8115	81972
	+/-	0	0	0	0
ot-rcp	main	63184	568	20804	84556
	#11325	63184	568	20804	84556
	+/-	0	0	0	0
libopenthread-rcp.a	main	9920	0	5060	14980
	#11325	9920	0	5060	14980
	+/-	0	0	0	0
libopenthread-radio.a	main	19249	0	238	19487
	#11325	19249	0	238	19487
	+/-	0	0	0	0

[codecov]

Codecov Report

Attention: Patch coverage is 71.21212% with 19 lines in your changes missing coverage. Please review.

Project coverage is 76.35%. Comparing base (4c0af02) to head (1bdf409).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/posix/platform/resolver.cpp	71.21%	19 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11325      +/-   ##
==========================================
+ Coverage   73.22%   76.35%   +3.12%     
==========================================
  Files         628      630       +2     
  Lines       97928    98717     +789     
==========================================
+ Hits        71711    75378    +3667     
+ Misses      26217    23339    -2878     

Files with missing lines	Coverage Δ
src/posix/platform/resolver.hpp	50.00% <ø> (ø)
src/posix/platform/resolver.cpp	68.36% <71.21%> (-1.84%)	⬇️

... and 297 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[abtink]

Thanks @yangsong-cnyn for adding this.

One suggestion about the title of the PR and commit message.

You have used [dns] dns solver to support ipv6 address.

• It is changing the Resolver class (not solver 😄).
• Using [dns] makes it sound like this is changing some DNS module within the OT core implementation.
• But this change is only related to the POSIX platform implementation and not part of the OT core. So, it's better to use [posix] instead.

I would suggest changing the title to [posix] update Posix::Resolver to support IPv6 addresses for servers.

[superwhd]

LGTM 👍

[abtink]

Thanks @yangsong-cnyn for the changed. Looks good overall.

Couple of smaller suggestions below:

[abtink]

LGTM. Thanks for all the changes.

Couple of smaller suggestions belwo:

[abtink]

The Resolver::GetTransaction(int aFd) does not seem to be used at all. I'm not sure why it was added.

Perhaps in a future (separate) PR, we can remove this to make the code simpler/cleaner?

[yangsong-cnyn]

I will remove it in next PR