refactor(qdrant): use async DocumentStore mixin tests

Closes #3052

Replaces duplicate async test implementations with the mixin classes
from haystack.testing.document_store and haystack.testing.document_store_async.

- Removes 19 tests now covered by the mixins
- Keeps all Qdrant-specific tests (hybrid search, sparse config, collection
  setup validation, vector preservation)

Author: SyedShahmeerAli12