[DMINQ]

Description

Allow NatsBroker.publish() and NatsBroker.request() to accept a JStream
object as the stream argument, alongside existing string names.

Normalize the object to its name before producer selection and middleware
execution. The target subject remains a separate argument, and sending
does not modify or declare the supplied stream.

Update return-type overloads, tests, and documentation.

Related to #3305.

Type of change

• New feature (a non-breaking change that adds functionality)
• Documentation update

Validation

• Real NATS with JetStream: publish delivery, PubAck stream name,
  and request/reply correlation checked for string and JStream arguments.
• Both object cases failed before implementation; all four cases passed after.
• Test-client and request-cleanup tests passed.
• Documentation example test and documentation checks passed.
• Ruff, mypy, Pyright, and Pyrefly passed.