tests: Add regression tests for unpickling nitypes 1.0.0 objects

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

Add tests for unpickling nitypes objects from previous releases.

I used the REPL to get the pickled_values, e.g.:

>>> pickle.dumps(DigitalWaveform(3, 2, extended_properties={"NI_LineNames": "port0/line1, port0/line0"}).signals[1])
b'\x80\x04\x95\xfa\x01\x00\x00\x00\x00\x00\x00\x8c\x10nitypes.waveform\x94\x8c\x15DigitalWaveformSignal\x94\x93\x94\x8c\x08builtins\x94\x8c\x07getattr\x94\x93\x94h\x00\x8c\x0fDigitalWaveform\x94\x93\x94\x8c\t_unpickle\x94\x86\x94R\x94K\x03K\x02\x8c\x05numpy\x94\x8c\x05dtype\x94\x93\x94\x8c\x02u1\x94\x89\x88\x87\x94R\x94(K\x03\x8c\x01|\x94NNNJ\xff\xff\xff\xffJ\xff\xff\xff\xffK\x00t\x94b\x87\x94}\x94(\x8c\x04data\x94\x8c\x16numpy._core.multiarray\x94\x8c\x0c_reconstruct\x94\x93\x94h\x0b\x8c\x07ndarray\x94\x93\x94K\x00\x85\x94C\x01b\x94\x87\x94R\x94(K\x01K\x03K\x02\x86\x94h\x10\x89C\x06\x00\x00\x00\x00\x00\x00\x94t\x94b\x8c\x13extended_properties\x94h\x00\x8c\x1aExtendedPropertyDictionary\x94\x93\x94)\x81\x94N}\x94\x8c\x0b_properties\x94}\x94\x8c\x0cNI_LineNames\x94\x8c\x18port0/line1, port0/line0\x94ss\x86\x94b\x8c\x18copy_extended_properties\x94\x89\x8c\x06timing\x94h\x05h\x00\x8c\x06Timing\x94\x93\x94h\x08\x86\x94R\x94(h\x00\x8c\x12SampleIntervalMode\x94\x93\x94K\x00\x85\x94R\x94NNNNt\x94}\x94\x86\x94R\x94u\x86\x94R\x94K\x01\x86\x94R\x94.'

Why should this Pull Request be merged?

Running https://pypi.org/project/griffe/ against 1.0.0 identified some changes that break pickle compatiblity.

What testing has been done?

Ran tests

[github-actions]

Test Results

    56 files  ±  0      56 suites  ±0   26m 15s ⏱️ +31s
 2 294 tests + 18   2 292 ✅ + 16   2 💤 + 2  0 ❌ ±0 
65 656 runs  +486  65 602 ✅ +432  54 💤 +54  0 ❌ ±0 

Results for commit 15ec9ac. ± Comparison against base commit 34019c6.

♻️ This comment has been updated with latest results.