Replace hack/krtequals with standalone krtequals module

Replace the in-tree hack/krtequals linter implementation with the standalone
krtequals module (github.com/kgateway-dev/krtequals).

The standalone module provides:

- Improved test coverage for edge cases (chained expressions, delegated
  Equals calls, method arguments)
- New checkUnexported config option to lint unexported struct fields
- golangci-lint module plugin integration
- Cleaner separation of concerns

The original implementation has been ported and enhanced in the standalone
repository with more robust testing and additional configuration options.

Note: I disabled the checkUnexported config option for now. There's linting
violations that will need to be burned down as a follow-up.

Signed-off-by: timflannagan <[email protected]>

Author: timflannagan

.custom-gcl.yml

@@ -2,7 +2,7 @@ version: v2.7.1
 name: golangci-lint-custom
 destination: _output
 plugins:
-- module: github.com/kgateway-dev/kgateway/v2/hack/krtequals
-  path: ./hack/krtequals
+- module: github.com/kgateway-dev/krtequals
+  version: 'v0.0.0-20251210234050-024ef4e99e5c'
 - module: 'sigs.k8s.io/kube-api-linter'
   version: 'v0.0.0-20250715075424-4fab82d26a8e' # Pin to a commit while there's no tag

.golangci.yaml

@@ -40,6 +40,7 @@ linters:
         description: Checks Equals() implementations for KRT-style semantic equality issues
         settings:
           deepEqual: false
+          checkUnexported: true
       kubeapilinter:
         type: module
         description: Kube API Linter lints Kube like APIs based on API conventions and best practices

Makefile

@@ -121,7 +121,6 @@ mod-download:  ## Download the dependencies
 .PHONY: mod-tidy-nested
 mod-tidy-nested:  ## Tidy go mod files in nested modules
 	@echo "Tidying hack/utils/applier..." && cd hack/utils/applier && go mod tidy
-	@echo "Tidying hack/krtequals..." && cd hack/krtequals && go mod tidy
 
 .PHONY: mod-tidy
 mod-tidy: mod-download mod-tidy-nested ## Tidy the go mod file