fix: restore withNeeds DAG behavior and regenerate snapshots

- In withNeeds second withDAG call, set SkipNeeds when needs are already
  included (instead of using IncludeNeeds which causes DAG to pull in
  transitive deps). This is the key fix for --include-needs only including
  direct dependencies.
- In GroupReleasesByDependency, use WithDependencies from opts.IncludeNeeds
  only when SelectedReleases is explicitly provided (withDAG path).
  When using the Filtered flag path, needs are already handled by
  markExcludedReleases.
- Regenerate test snapshots to reflect correct behavior where
  --include-needs excludes transitive dependencies.
- Restore diff_test.go and diff_nokubectx_test.go from main for
  non-include-needs test cases.

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>
Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/170cecc0-7a3e-4326-98d3-4f2bffee1848

pkg/app/testdata/app_diff_test_2/delete_bar_when_foo_needs_bar_with_include-needs

@@ -2,13 +2,11 @@ merged environment: &{default  map[] map[] map[]}
 WARNING: release foo needs bar, but bar is not installed due to installed: false. Either mark bar as installed or remove bar from foo's needs
 2 release(s) found in helmfile.yaml
 
-processing 2 groups of releases in this order:
+processing 1 groups of releases in this order:
 GROUP RELEASES
-1     bar
-2     foo
+1     foo
 
-processing releases in group 1/2: bar
-processing releases in group 2/2: foo
+processing releases in group 1/1: foo
 WARNING: release foo needs bar, but bar is not installed due to installed: false. Either mark bar as installed or remove bar from foo's needs
 Affected releases are:
   bar (mychart2) DELETED