[Hosts] Duplicate check improvement

[davidegiacometti]

Summary of the Pull Request

The duplicate check logic degraded overtime with the additional logics introduced (max 9 hosts per line, etc..).

• This PR aims to move the current logic from the view model to a dedicated service and make it async.
• Since a typical usage of the hosts file is to block domains mapping them to 0.0.0.0 I have added 0.0.0.0 (and IPv6 equivalent) to the list of loopback addresses in order to skip the check.

PR Checklist

• Closes: Unexpted behaviour: Hosts File Editor freezes when trying to add a new entry into a hosts file with 50k entries #29952 The "Consider loopback addresses as duplicates" setting does not affect hosts-records whose address is "0.0.0.0" #31483
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated
• New binaries: Added on the required places
  • JSON for signing for new binaries
  • WXS for installer for new binaries and localization folder
  • YML for CI pipeline for new test projects
  • YML for signed pipeline
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

• Manually tested with a hosts file containing more than 100K entries:
  • Verified that duplicate check is working as before but in an async way
  • Tested file reload
  • Tested "Consider loopback addresses as duplicate" enable/disable (it does trigger a hosts file reload)
  • Edited an entry with a huge number of duplicates and verified that UI doesn't freeze

[htcfreek]

RFC says short version: ::

https://www.rfc-editor.org/rfc/rfc4291#section-2.5.2

[jaimecbernardo]

Not quite sure about all rules for duplicates, but changes look good to me and the tests I did seem to make it work as it was before.
Thank you for the contribution.