Message-store

Changes:
- Implement basic integration testing with low coverage initially
- `max_bytes` was incorrectly associated with `max_msg_size`, we now default to 1GB for the former and 4MB for the latter
- Retry publish/fetch on `nats.js.errors.NoStreamResponseError`
- Error codes are numbers, not strings
- If `WPI` message fails, report why
- Also reduce `WPI` interval to 10 seconds, so two have to fail to hit the default 30s window
- Bump `nats-py` to 2.9.0

- Implement sane retries during periods of degradation, via https://zencastr.atlassian.net/browse/PL-5174
- Actively delete ephemeral consumers after they're used
- Expose `.timestamp` property in `MessageFromSubscription` in order track time between publishing and processing

- add `max_bytes` parameter to MessageStore initialization

Install `nats-py[nkeys]` instead of just `nats-py`. Also add license and ensure mypy and ruff tests pass.

First ever release of python's version of message store