chore: simplify + modernize (Go 1.26)

[rustatian]

Cleanup pass from a multi-plugin review (/simplify + /use-modern-go Go 1.26 + /review).

Changes

• Bug/dead code: resolveIP XFF branch had a dead, inverted guard if len(fwd) < s (unreachable — strings.Index already returned s >= 0). Replaced the whole Index+slice dance with strings.Cut, which returns the full string when no comma is present.
• Modern Go: range-over-value (for _, subnet := range p.trusted) instead of index loop.
• Dead code: removed the unused exported Cidrs type (and its now-unused net import) from config.go.
• Hygiene: moved the test-only inc() helper into trusted_test.go; collapsed a single-entry var() block.

Deps

go get -u all (root + tests) and go work sync were no-ops — module already current.

Summary by CodeRabbit

• Refactor

  • Simplified IP header parsing logic for improved efficiency
  • Optimized trusted subnet membership iteration
  • Removed unused exported type from package API

• Tests

  • Added test helper for IP iteration validation

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR refactors the proxy IP parser package by removing the exported Cidrs type from the public API, relocating an internal inc() helper from plugin code to tests, simplifying IP header parsing with strings.Cut, and applying minor code-style improvements to variable declarations and loop iteration patterns.

Changes

Core Refactoring and API Cleanup

Layer / File(s)	Summary
Public API cleanup config.go	Removes the exported Cidrs type alias and net import, leaving only the Config struct as the public interface.
Helper relocation and IP parsing simplification plugin.go, trusted_test.go	Moves the inc() helper function from plugin.go to trusted_test.go where it is used; simplifies X-Forwarded-For header parsing in resolveIP by replacing manual strings.Index and slicing logic with strings.Cut.
Code style refactoring plugin.go	Refactors forwardedRegex from a parenthesized var (...) block to a single var assignment; converts the trusted-subnet membership loop from index-based to range-based iteration while preserving logic.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A helper hops away to tests where it belongs,
Parsing gets trimmer with strings that sing songs,
Vars shrink and loops flow in ranges so clean,
API unwrapped—the cleanest we've seen!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately reflects the main objectives: cleanup and modernization for Go 1.26 compatibility.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The PR description clearly explains the reasoning (cleanup pass with linting suggestions), provides comprehensive change descriptions with categorization (Bug/dead code, Modern Go, Dead code, Hygiene), and includes verification steps performed.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/cleanup-modernize-deps

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[Copilot]

Pull request overview

Cleanup pass on the proxy_ip_parser RoadRunner middleware: removes dead/unreachable code, modernizes a loop, and tidies declarations. No behavior changes intended.

Changes:

• Simplify XFF parsing in resolveIP using strings.Cut, eliminating an unreachable len(fwd) < s guard.
• Use range-over-value in the trusted-subnet loop; collapse the single-entry var() block.
• Remove the unused exported Cidrs type (and net import) from config.go; move the test-only inc() helper into trusted_test.go.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
plugin.go	Simplify XFF branch with strings.Cut; range-over-value loop; collapse var block; drop inc() helper.
trusted_test.go	Host the test-only inc() helper now removed from plugin.go.
config.go	Drop unused Cidrs type and net import.

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