Add task sdk integration tests for ti rtif, heartbeat, state transitions

[amoghrajesh]

Next part to: #57056

Expanding the tests to cover more breadth in the task instance space itself.

The tests now added cover these:

1. test_ti_set_rtif

   • Sets Rendered Task Instance Fields
   • Tests the endpoint: PUT /task-instances/{id}/rtif

2. test_ti_heartbeat

   • Sends heartbeat for a running task instance
   • Tests the endpoint: PUT /task-instances/{id}/heartbeat
   • Special Implementation: Fetches actual worker PID/hostname from Core API, then patches get_hostname() to match, ensuring heartbeat validation succeeds
   • Validates PID/hostname matching logic

3. 7test_ti_state_transitions

   • Tests state transition to terminal state (FAILED)
   • Tests the endpoint: PATCH /task-instances/{id}/state
   • Validates the finish() method
   • Will expand this further to cover deferred as well as up_for_retry

What's Next

Following the testing roadmap, the next priorities are:

1. XCom operations tests
2. Variable operations tests
3. Connection operations tests
4. DAG Run operations tests
5. Asset operations tests

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[jason810496]

Nice! LGMT overall!

[potiuk]

nice!