fix: clean up deleting restore PVCs

[weicao]

Summary

• handle a deleting restore PVC before validating its source Backup
• stop and wait for the execution Restore before removing populate dependents
• keep the target PVC finalizer while owned populate Jobs or the helper PVC still exist
• release the target finalizer only after a fresh reconcile confirms the dependents are absent
• propagate every transient deletion-cleanup API failure through the outer reconciler even when the PVC already has a Populating condition
• preserve the existing non-deletion cleanup behavior for bound PVC completion

Fixes #10606.

Retry contract

A deleting PVC is still owned by the volume-populator controller until cleanup converges. Ordinary API errors from execution-Restore cleanup, Job cleanup, helper-PVC cleanup, or target-finalizer removal must therefore reach controller-runtime and be retried. The outer handler keys this rule from deletionTimestamp; it deliberately does not re-check the in-memory finalizer because Cleanup removes that local value before attempting the final Patch, and a failed Patch means the persisted finalizer still exists.

The existing Populating-condition suppression remains limited to non-deleting PVCs whose external controller owns subsequent progress.

Tests

• focused cleanup tests cover deletion ordering, dependent absence, and all eight API failure points
• the eight-point failure matrix enters through the complete Reconcile path, asserts the injected error reaches controller-runtime, and proves the persisted target finalizer remains
• KUBEBUILDER_ASSETS='<envtest 1.26.1 assets>' go test ./controllers/dataprotection -count=1
• focused go test -race for deletion and outer-handler cases
• go vet ./controllers/dataprotection
• git diff --check

Validation on exact head 35f7f55c14e6c76208aab161d11c3ad35313e359 is green. Runtime environment coverage remains N=0.

Supersedes #10604, which was closed when its non-conforming source branch was renamed.

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[codecov]

Codecov Report

❌ Patch coverage is 96.77419% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.94%. Comparing base (12611aa) to head (35f7f55).
⚠️ Report is 34 commits behind head on main.

Files with missing lines	Patch %	Lines
...llers/dataprotection/volumepopulator_controller.go	96.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10605      +/-   ##
==========================================
- Coverage   63.97%   63.94%   -0.03%     
==========================================
  Files         520      520              
  Lines       62887    62942      +55     
==========================================
+ Hits        40229    40249      +20     
- Misses      19071    19101      +30     
- Partials     3587     3592       +5     

Flag	Coverage Δ
unittests	63.94% <96.77%> (-0.03%)	⬇️

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[leon-ape]

Closing this PR as superseded by #10777.

#10605 established several useful cleanup invariants: stop the execution Restore before dependent cleanup, observe Restore/helper absence before releasing the target PVC finalizer, and keep cleanup API failures retryable. Those invariants should be retained, but the cleanup must be coordinated by the Cluster restore lifecycle rather than by a parallel PVC-local deletion workflow.

#10777 provides the stronger ownership model: a Cluster restore finalizer, Cluster UID identity, verified owner references, direct API-server reads, ordered Cluster-wide teardown, and legacy-resource adoption. It is now the authoritative implementation path. Direct deletion of an active restore target PVC is treated as an unsupported/destructive management operation and should remain fail-closed instead of triggering autonomous DP cleanup.

Any remaining safety checks and failure-path tests from this PR should be carried into #10777 where they apply. No commits from this PR need to be merged directly.