Proposed changes

Problem: createPortConflictResolver carried a //nolint:gocyclo exception (plus a maintainer FIXME to refactor before 2.7). Its returned closure packed all per-port conflict-detection logic into a single deeply nested function, hurting readability.

Solution: Extracted the closed-over state into a portConflictResolver struct and split the conflict handling into focused methods (resolveProtocolGroupConflict, resolveSameProtocolGroupConflict) plus three small invalidate* helpers that replace the repeated "mark listener invalid + append condition" blocks. Behavior is unchanged; the //nolint:gocyclo directive and the FIXME comment are removed.

Testing:

• go test ./internal/controller/state/graph/... passes unchanged (existing table-driven conflict tests).
• golangci-lint run ./internal/controller/state/graph/... reports 0 issues — every resulting function is now under the configured gocyclo min-complexity: 15, so the nolint removal holds.
• gofmt + go vet clean.

This is a first step toward #5253 (one of the ~14 nolint:gocyclo functions — the one flagged with a FIXME(bjee19)). Happy to follow up with the remaining sites in separate PRs.

related: #5253

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

NONE