Implement connect() and disconnect()

[mikeprosserni]

What does this Pull Request accomplish?

This PR implements Panel.connect() and Panel.disconnect(), allowing the Panel to connect to a PythonPanelServer. The port to connect to is determined by the specific subclass of Panel, and how it overrides _resolve_service_address().

The StreamlitPanel uses the DiscoveryClient to find the port for the "ni.pythonpanel.v1.PythonPanelService".

I also added a PortPanel for testing. This allows test code to connect to a server at a specified port. This is used in conjunction with a new FakePythonPanelServicer that trivially implements the PythonPanelServer interface.

Why should this Pull Request be merged?

Implements AB#3095680 - Implement connect() and disconnect()

What testing has been done?

I added tests for the new FakePythonPanelServicer, just to ensure it accepts requests and returns responses.

Also, the preexisting tests for Panel now use the new PortPanel (with a pytest fixture) to connect to the FakePythonPanelServicer.

[github-actions]

Test Results

10 files  ± 0  10 suites  ±0   5s ⏱️ ±0s
 8 tests + 5   8 ✅ + 5  0 💤 ±0  0 ❌ ±0 
80 runs  +50  80 ✅ +50  0 💤 ±0  0 ❌ ±0 

Results for commit 5f873b7. ± Comparison against base commit 13e7f3c.

This pull request removes 3 and adds 8 tests. Note that renamed tests count towards both.

tests.unit.test_panel ‑ test___connected_panel___set_value___gets_same_value
tests.unit.test_panel ‑ test___streamlit_panel___has_panel_id_and_panel_uri
tests.unit.test_panel ‑ test___with_panel___set_value___gets_same_value

tests.unit.test_python_panel_service_stub ‑ test___connect___gets_response
tests.unit.test_python_panel_service_stub ‑ test___disconnect___gets_response
tests.unit.test_python_panel_service_stub ‑ test___get_value___gets_response
tests.unit.test_python_panel_service_stub ‑ test___set_value___gets_response
tests.unit.test_streamlit_panel ‑ test___connected_panel___set_value___gets_same_value
tests.unit.test_streamlit_panel ‑ test___first_connect_fails___connect___gets_value
tests.unit.test_streamlit_panel ‑ test___panel___has_panel_id_and_panel_uri
tests.unit.test_streamlit_panel ‑ test___with_panel___set_value___gets_same_value

♻️ This comment has been updated with latest results.

[csjall]

Take a look at pin map client code. A couple of notable things:

• Optionally passes in discovery client, channel pool, or channel. Allows caller to specify their own. Create these if not provided.
• Lazily creates stub before calling rpc method.
• Uses lock to synchronize lazy creation. Ensure that we are not creating multiple stubs at the same time.
• Create requests using method parameters. Return value/tuples from response.
• Uses logger to log debug traces

[bkeryan]

• Optionally passes in discovery client, channel pool, or channel. Allows caller to specify their own. Create these if not provided.

Note that channel is really for unit testing.

[bkeryan]

Approved with suggestions