waveform: Implement append

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

Add AnalogWaveform.append(), which accepts:

• A np.ndarray, AnalogWaveform, or a sequence of AnalogWaveforms
• An optional sequence of irregular timestamps

Add AnalogWaveform._base_timing, to enable internal-only polymorphic timing access.

Add BaseTiming._append_timing, which appends irregular timestamps. This class is still immutable.

Add a _sample_interval subpackage defining the SampleIntervalMode enum and new SampleIntervalStrategy classes.

Why should this Pull Request be merged?

Closes AB#3082119 - Add waveform appending

What testing has been done?

Ran unit tests
Used test coverage to guide error testing

[github-actions]

Test Results

   10 files  ±  0     10 suites  ±0   22s ⏱️ +4s
  350 tests + 82    344 ✅ + 81   6 💤 + 1  0 ❌ ±0 
3 500 runs  +820  3 440 ✅ +810  60 💤 +10  0 ❌ ±0 

Results for commit b54f0a1. ± Comparison against base commit f33ea2f.

This pull request removes 2 and adds 84 tests. Note that renamed tests count towards both.

tests.unit.waveform._timing.test_precision ‑ test___timestamps___create_with_irregular_interval___creates_waveform_timing_with_timestamps
tests.unit.waveform._timing.test_standard ‑ test___timestamps___create_with_irregular_interval___creates_waveform_timing_with_timestamps

tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets0-right_offsets0]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets1-right_offsets1]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets2-right_offsets2]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets3-right_offsets3]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets4-right_offsets4]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets5-right_offsets5]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets6-right_offsets6]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets7-right_offsets7]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets8-right_offsets8]
tests.unit.waveform._timing.test_precision ‑ test___monotonic_timestamps___append_timing___appends_timestamps[left_offsets9-right_offsets9]
…

♻️ This comment has been updated with latest results.

@csjall is OOO, attending the NI Connect conference. I have addressed his feedback and @jfriedri-ni has approved these changes.