fix: stop fixed-width string decoding at first NUL

[SaiDeepikaKuchibhotla]

Proposed changes

Description

Fixes an issue where converting WFM waveform data to CSV could raise a UnicodeDecodeError when fixed-width axis-unit fields contained non-UTF-8 padding bytes after a valid null terminator. This can occur with WFM files generated by a Tektronix DPO71254C.
For example, the axis-unit fields may contain:

• s followed by a null terminator and non-UTF-8 padding bytes
• V followed by a null terminator and non-UTF-8 padding bytes

Previously, String.__str__() decoded the entire fixed-width byte field before removing trailing null characters:

self.decode("utf_8").rstrip("\x00")

Addresses #211

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Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.91%. Comparing base (27dd5d8) to head (2d1c843).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #220   +/-   ##
=======================================
  Coverage   82.91%   82.91%           
=======================================
  Files          33       33           
  Lines        2763     2763           
  Branches      359      359           
=======================================
  Hits         2291     2291           
  Misses        337      337           
  Partials      135      135           

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[nfelt14]

Why did you need to change this?

[github-actions]

Test Results (ubuntu)

path	passed	skipped	subtotal
tests/test_fastframe.py	24		24
tests/test_fastframe_analog_waveform.py	13	3	16
tests/test_fastframe_digital_waveform.py	11		11
tests/test_tm_data_types.py	20	1	21
tests/test_tss_reader.py		3	3
TOTAL	68	7	75

tests/test_fastframe_analog_waveform.py

('/home/runner/work/tm_data_types/tm_data_types/tests/test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: /home/runner/work/tm_data_types/tm_data_types/archive/test_wfms/FastFrame_waveforms/FF5MhzX100From5Series.wfm')('/home/runner/work/tm_data_types/tm_data_types/tests/test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: /home/runner/work/tm_data_types/tm_data_types/archive/test_wfms/FastFrame_waveforms/FF1MX5005Series.wfm')('/home/runner/work/tm_data_types/tm_data_types/tests/test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: /home/runner/work/tm_data_types/tm_data_types/archive/test_wfms/FastFrame_waveforms/FF1MX1095Series.wfm')

tests/test_tm_data_types.py

('/home/runner/work/tm_data_types/tm_data_types/tests/test_tm_data_types.py', 549, 'Skipped: Skipping 1G test in GitHub Actions environment')

tests/test_tss_reader.py

('/home/runner/work/tm_data_types/tm_data_types/tests/test_tss_reader.py', 16, 'Skipped: TSS fixture missing')('/home/runner/work/tm_data_types/tm_data_types/tests/test_tss_reader.py', 25, 'Skipped: TSS fixture missing')('/home/runner/work/tm_data_types/tm_data_types/tests/test_tss_reader.py', 35, 'Skipped: TSS fixture missing')

Link to workflow run

[github-actions]

Test Results (windows)

path	passed	skipped	subtotal
tests\test_fastframe.py	24		24
tests\test_fastframe_analog_waveform.py	13	3	16
tests\test_fastframe_digital_waveform.py	11		11
tests\test_tm_data_types.py	20	1	21
tests\test_tss_reader.py		3	3
TOTAL	68	7	75

tests\test_fastframe_analog_waveform.py

('D:\\a\\tm_data_types\\tm_data_types\\tests\\test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: D:\\a\\tm_data_types\\tm_data_types\\archive\\test_wfms\\FastFrame_waveforms\\FF5MhzX100From5Series.wfm')('D:\\a\\tm_data_types\\tm_data_types\\tests\\test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: D:\\a\\tm_data_types\\tm_data_types\\archive\\test_wfms\\FastFrame_waveforms\\FF1MX5005Series.wfm')('D:\\a\\tm_data_types\\tm_data_types\\tests\\test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: D:\\a\\tm_data_types\\tm_data_types\\archive\\test_wfms\\FastFrame_waveforms\\FF1MX1095Series.wfm')

tests\test_tm_data_types.py

('D:\\a\\tm_data_types\\tm_data_types\\tests\\test_tm_data_types.py', 549, 'Skipped: Skipping 1G test in GitHub Actions environment')

tests\test_tss_reader.py

('D:\\a\\tm_data_types\\tm_data_types\\tests\\test_tss_reader.py', 16, 'Skipped: TSS fixture missing')('D:\\a\\tm_data_types\\tm_data_types\\tests\\test_tss_reader.py', 25, 'Skipped: TSS fixture missing')('D:\\a\\tm_data_types\\tm_data_types\\tests\\test_tss_reader.py', 35, 'Skipped: TSS fixture missing')

Link to workflow run

[github-actions]

Test Results (macos)

path	passed	skipped	subtotal
tests/test_fastframe.py	24		24
tests/test_fastframe_analog_waveform.py	13	3	16
tests/test_fastframe_digital_waveform.py	11		11
tests/test_tm_data_types.py	20	1	21
tests/test_tss_reader.py		3	3
TOTAL	68	7	75

tests/test_fastframe_analog_waveform.py

('/Users/runner/work/tm_data_types/tm_data_types/tests/test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: /Users/runner/work/tm_data_types/tm_data_types/archive/test_wfms/FastFrame_waveforms/FF5MhzX100From5Series.wfm')('/Users/runner/work/tm_data_types/tm_data_types/tests/test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: /Users/runner/work/tm_data_types/tm_data_types/archive/test_wfms/FastFrame_waveforms/FF1MX5005Series.wfm')('/Users/runner/work/tm_data_types/tm_data_types/tests/test_fastframe_analog_waveform.py', 73, 'Skipped: Corpus file missing: /Users/runner/work/tm_data_types/tm_data_types/archive/test_wfms/FastFrame_waveforms/FF1MX1095Series.wfm')

tests/test_tm_data_types.py

('/Users/runner/work/tm_data_types/tm_data_types/tests/test_tm_data_types.py', 549, 'Skipped: Skipping 1G test in GitHub Actions environment')

tests/test_tss_reader.py

('/Users/runner/work/tm_data_types/tm_data_types/tests/test_tss_reader.py', 16, 'Skipped: TSS fixture missing')('/Users/runner/work/tm_data_types/tm_data_types/tests/test_tss_reader.py', 25, 'Skipped: TSS fixture missing')('/Users/runner/work/tm_data_types/tm_data_types/tests/test_tss_reader.py', 35, 'Skipped: TSS fixture missing')

Link to workflow run