feat: GraphQL subscriptions via Strawberry + Channels (#764)

[Jessepriase]

Implementation was already in place across schema.py, asgi.py and subscription_middleware.py. This commit completes the issue by:

requirements.txt:

• Upgrade strawberry-graphql to strawberry-graphql[channels]==0.289.0 to formally declare the channels extras dependency (channels, daphne, channels_redis were already present individually)

test_graphql_subscriptions.py — integration tests covering all acceptance criteria without requiring a live WebSocket stack:

Schema shape

• Subscription type exists and is named 'Subscription'
• contractEvents field is present with contractId argument
• Existing notifications field is still present

Resolver type safety

• contract_events is an AsyncGenerator (async def ... yield)
• notifications is also an AsyncGenerator

Channel lifecycle

• group_add called with 'events_{contract_id}' group name on subscribe
• group_discard called in finally block when generator is closed
• group_discard called even when channel layer raises mid-loop
• No channel layer configured: resolver exits gracefully without error

End-to-end event flow

• Message published to channel group causes resolver to yield ContractEvent
• ContractEvent.DoesNotExist is swallowed; generator continues

HTTP query regression

• contracts, events, and introspection queries all still work

Rate limiting (SubscriptionRateLimitMiddleware)

• Allows up to 5 concurrent connections per IP
• Rejects 6th connection with close code 4429
• Allows connections below the limit
• Decrements counter on close
• IP extraction: X-Forwarded-For takes precedence over client address
• Non-WebSocket scopes bypass middleware unchanged

ASGI routing

• GraphQLWSConsumer importable from strawberry.channels
• application is a ProtocolTypeRouter
• Schema object exposes a subscription type
  closes GraphQL Subscriptions via Strawberry + Channels #764

[drips-wave]

@Jessepriase Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[DokaIzk]

@Jessepriase CI checks are failing, kindly resolve