Add close() and close_async() to QdrantDocumentStore

[ErenAta16]

Closes #1628

QdrantDocumentStore lazily creates a QdrantClient and AsyncQdrantClient on first use but never released either one, so long-running processes and test suites had no way to release the underlying HTTP connections.

WeaviateDocumentStore, PineconeDocumentStore, and ValkeyDocumentStore already expose this same close()/close_async() pair (introduced in #2891), so this follows the same convention: each method releases its respective client and resets it to None, letting it be lazily re-initialized on the next call.

Usage after this PR:

document_store = QdrantDocumentStore(...)
try:
    document_store.write_documents(docs)
finally:
    document_store.close()

Test plan: four new tests covering the sync and async client, both the normal case (initialize, close, verify it's None, confirm lazy re-initialization still works) and the safety case (calling close before the client was ever created should be a no-op). All use Qdrant's :memory: mode, so no external server is required.

Verified locally: all 260 existing + new tests pass, ruff check / ruff format --check are clean, and mypy reports no issues.

[github-actions]

Coverage report (qdrant)

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
integrations/qdrant/src/haystack_integrations/document_stores/qdrant
document_store.py
Project Total

This report was generated by python-coverage-comment-action