Add Digital Stream Writer tests

[zhindes]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

This ensures we have a test per method of the Digital stream writer classes. These tests use digital loopback to validate that the data made it all the way through the Python/C bindings correctly to the underlying driver.

other miscellany

• better workaround for Indexing PhysicalChannelCollection fails for slices and strings containing a list/range of channels #392
• more pythonic code for initializing a list of a single value

Why should this Pull Request be merged?

This will give us confidence that we haven't broken anything as we refactor parts of the Python / C bindings.

What testing has been done?

> poetry run ni-python-styleguide fix tests && poetry run ni-python-styleguide lint tests && poetry run pytest -rs -k test_stream_writers_do
===================================== test session starts ======================================
platform win32 -- Python 3.9.13, pytest-8.0.2, pluggy-1.4.0
rootdir: C:\dev\nidaqmx-python
configfile: pyproject.toml
testpaths: tests
plugins: cov-4.1.0, mock-3.12.0
collected 1951 items / 1897 deselected / 54 selected

tests\component\test_stream_writers_do.py ............................................... [ 87%]
.......                                                                                   [100%]

============================= 54 passed, 1897 deselected in 18.00s =============================

(I also checked test_stream_writers_ao and test_stream_readers_di for the minor fixes there.)

[github-actions]

Test Results

    30 files  ±    0      30 suites  ±0   37m 8s ⏱️ - 1m 21s
 2 004 tests +   74   1 667 ✅ + 12    337 💤 + 62  0 ❌ ±0 
31 740 runs  +1 060  26 810 ✅ +170  4 930 💤 +890  0 ❌ ±0 

Results for commit f0e5a5b. ± Comparison against base commit df7366e.

♻️ This comment has been updated with latest results.