chore: harden Dapr Redis integration fixture loading

[Aphroq]

Summary

This pull request fixes the Dapr Redis integration fixture so the sidecar can read the mounted component file reliably and the test waits for the statestore component to be registered before using it.

Test plan

• uv run pytest tests/extensions/memory/test_dapr_redis_integration.py -q

Issue number

N/A

Checks

• I've added new tests (if relevant)
• I've added/updated the relevant documentation
• I've run make lint and make format
• I've made sure tests pass

[seratch]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

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