add completion of node ids (test classes/functions) for argcomplete

Often enough I want to run a single test via the CLI. Tab completion (with or without argcomplete) works fine to get to the file, but completion for node ids (test classes/functions) is not supported.
As a workaround I either copy-paste the name of the test from my IDE, or do a --collect-only -q to copy-paste from there.

What I'd like to pytest to do, is that if I add a double colon :: after the file name, I get tab completion for the node ids (test classes/functions) in the file.

So if I have:

test_file.py
|- test_func_one
|- test_func_two
|- TestClass
    |- test_method

• completion of pytest test_file.py:: would display test_func_one test_func_two TestClass
• completion of pytest test_file.py::test_o would result in pytest test_file.py::test_one
• completion of pytest test_file.py::TestClass:: would result in pytest test_file.py::TestClass::test_method

Open question: what to do with parameterized tests? --collect-only shows them as separate tests, but I'm not aware of a way to run them from the CLI as a separate test.

Depending on the complexity I might be interested in trying to implement this. (It would be my first contribution to the pytest codebase.) I assume implementing this completion would involve collecting all tests in src/_pytest/_argcomplete.py in FastFilesCompleter or in a new completer, if the path ends with a double colon?

Start in src/_pytest/_argcomplete.py, especially FastFilesCompleter, and inspect how pytest --collect-only -q represents node ids. Define completion after a file path and after a class node, including the parameterized-test question raised in the issue. Done means the shown file, function, and class-method completion examples work from the CLI.