fix: ensure OCI charts are prepared for needed releases with --include-needs (#2663)

fix: ensure OCI charts are prepared for needed releases with --include-needs (#923)

When using --include-needs with a selector, releases included via needs
must have their charts prepared (pulled/exported) before diff/sync/apply
can process them. The core fix (ChartPrepareOptions.IncludeTransitiveNeeds
= c.IncludeNeeds()) was already in place, but ForEachState calls in
Diff/Template/Lint/Unittest/Sync/Apply still passed c.IncludeTransitiveNeeds()
instead of c.IncludeNeeds(), creating an inconsistency that would resurface
if SetFilter(true) were ever added.

Changes:
- Use c.IncludeNeeds() in ForEachState for all commands supporting
  --include-needs (Diff, Template, Lint, Unittest, Sync, Apply, Doctor)
- Doctor is the only command with SetFilter(true), so this fixes a real
  bug: helmfile doctor --include-needs was silently ignored for filtering
- Add explanatory doc comment on ForEachState parameter semantics
- Enhance exectest.Helm.ChartPull to create minimal chart files and track
  pulls, enabling OCI chart testing
- Add resetChartCacheForTest() for test isolation from global chart cache
- Add regression tests for issue #923

Signed-off-by: yxxhero <11087727+yxxhero@users.noreply.github.com>
Signed-off-by: yxxhero <aiopsclub@163.com>

pkg/state/state.go

@@ -5356,6 +5356,13 @@ func (st *HelmState) addToChartCache(key ChartCacheKey, path string) {
 	downloadedCharts[key] = path
 }
 
+// resetChartCacheForTest clears the global chart cache. For testing only.
+func resetChartCacheForTest() {
+	downloadedChartsMutex.Lock()
+	defer downloadedChartsMutex.Unlock()
+	downloadedCharts = make(map[ChartCacheKey]string)
+}
+
 // isSharedCachePath returns true if the chartPath is within the shared cache directory.
 // Charts in the shared cache should not be deleted during refresh to prevent race conditions
 // when multiple processes are using the same cached chart.