feat: add search, sms, and delivery namespaces to CommuneClient

Adds three new namespaces to both CommuneClient and AsyncCommuneClient
that correspond to existing backend API endpoints:

  - client.search.threads(query, inbox_id, limit) → /v1/search/threads
  - client.sms.send(to, body) → /v1/sms/send
  - client.delivery.metrics(inbox_id, period) → /v1/delivery/metrics
  - client.delivery.suppressions(inbox_id) → /v1/delivery/suppressions
  - client.delivery.events(inbox_id, event_type) → /v1/delivery/events

Also adds five new typed response models: SearchResult, SmsSendResult,
DeliveryMetrics, DeliverySuppression, DeliveryEvent.

Bumps to 0.3.0.

chore: expand PyPI keywords and classifiers for discoverability

chore: expand PyPI keywords and classifiers for discoverability

chore: expand PyPI keywords and classifiers for discoverability