refactor: centralize DNS response creation logic with helper functions

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.16%. Comparing base (0c35f21) to head (254a16c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1942      +/-   ##
==========================================
- Coverage   90.22%   90.16%   -0.06%     
==========================================
  Files          90       90              
  Lines        6473     6458      -15     
==========================================
- Hits         5840     5823      -17     
- Misses        493      495       +2     
  Partials      140      140              

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[Copilot]

Pull Request Overview

This PR refactors DNS response creation logic by introducing centralized helper functions in a new model/response_helpers.go file. The refactoring improves code maintainability by standardizing how DNS responses are created across different resolver types, reducing code duplication and making the response creation pattern more explicit and consistent.

Key changes:

• Introduced four helper functions (NewResponseWithReason, NewResponseWithAnswers, NewResponseWithRcode, NewEmptyResponse) to centralize DNS response creation patterns
• Updated multiple resolvers to use these helpers instead of manually creating dns.Msg instances and calling SetReply/SetRcode
• Modified createServFailResponseDNSSEC to accept *model.Request instead of *dns.Msg for consistency with the new helpers

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
model/response_helpers.go	New file containing four helper functions for standardized DNS response creation with different initialization patterns
resolver/hosts_file_resolver.go	Refactored to use NewResponseWithAnswers for PTR record responses and simplified resolve method to return []dns.RR instead of *dns.Msg
resolver/fqdn_only_resolver.go	Replaced manual response creation with NewEmptyResponse for NXDOMAIN responses
resolver/filtering_resolver.go	Replaced SetRcode pattern with NewResponseWithRcode helper
resolver/dnssec_resolver.go	Updated createServFailResponseDNSSEC to accept *model.Request and use NewResponseWithRcode helper
resolver/dnssec_resolver_test.go	Updated test calls to createServFailResponseDNSSEC to pass *model.Request instead of *dns.Msg
resolver/custom_dns_resolver.go	Refactored to use NewResponseWithAnswers and NewResponseWithReason helpers, removing manual dns.Msg creation
resolver/blocking_resolver.go	Replaced manual response creation with NewResponseWithReason helper for blocked requests

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