Add Huawei Drive support

Add Huawei Drive backend implementation and tests

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Nick Craig-Wood <nick@craig-wood.com>

fstest/test_all/config.yaml

@@ -660,6 +660,10 @@ backends:
    ignoretests:
      - cmd/bisync
      - cmd/gitannex
+ - backend: "huaweidrive"
+   remote: "TestHuaweiDrive:"
+   fastlist: true
+   listretries: 5
  - backend: "shade"
    remote: "TestShade:"
    fastlist: false