Rename waveform.unit_description to units

[mikeprosserni]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable.
• I've added tests applicable for this pull request

What does this Pull Request accomplish?

In the latest version of nitypes, AnalogWaveform.unit_description has been renamed to "units". This PR uptakes the latest version, and fixes the usages.

Why should this Pull Request be merged?

ni/nitypes-python#168

What testing has been done?

These tests now pass:

tests/component/test_stream_readers_ai.py:195: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:214: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:235: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:303: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:327: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:347: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:372: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:392: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:487: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:513: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:545: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:610: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:637: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:669: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]
tests/component/test_stream_readers_ai.py:694: error: "AnalogWaveform[floating[_64Bit]]" has no attribute "unit_description"  [attr-defined]

[github-actions]

Test Results

    38 files  ±0      38 suites  ±0   1h 2m 55s ⏱️ + 1m 42s
 2 590 tests ±0   2 190 ✅ ±0    400 💤 ±0  0 ❌ ±0 
46 490 runs  ±0  39 764 ✅ ±0  6 726 💤 ±0  0 ❌ ±0 

Results for commit f0aef54. ± Comparison against base commit 911b137.