Implement PZN8

[fostermaier]

Implement PZN8 code generation. Fixes#167.

• keeping PZN for PZN7, implementing PZN8 for PZN8
• checksum is commonly part of the PZN* code. Hence, we verify or append the checksum based on the length of the supplied PZN7 or PZN8 code.
• explicit error messages concerning code length for both classes respectively
• different checksum calculation for PZN8. see http://www.pruefziffernberechnung.de/P/PZN.shtml

usage

check code length

>>> PZN('12345678')
barcode.errors.NumberOfDigitsError: PZN7 must have 6 digits (excluding checksum) or 7 digits (including checksum), not 8.
>>> PZN8('123456789')
barcode.errors.NumberOfDigitsError: PZN8 must have 7 digits (excluding checksum) or 8 digits (including checksum), not 9.

auto-append checksum

>>> PZN('123456')
<PZN7('PZN-1234562')>
>>> PZN8('1234567')
<PZN8('PZN-12345678')>

verify checksum if supplied

>>> PZN('1234568')
barcode.errors.BarcodeError: Checksum (last digit) is not valid for the supplied PZN7 code.
>>> PZN('1234562')
<PZN7('PZN-1234562')>

resources (mostly german)

• checksum details http://www.pruefziffernberechnung.de/P/PZN.shtml
• official specification https://www.ifaffm.de/de/ifa-codingsystem/codierung-pzn-code_39.html

samples

PZN7: https://barcode.tec-it.com/de/Health_PZN7

PZN8: https://www.softmatic.com/de/barcode-code-pzn.html

[codecov]

Codecov Report

Base: 80.63% // Head: 80.06% // Decreases project coverage by -0.56%⚠️

Coverage data is based on head (25cf372) compared to base (3643a65).
Patch coverage: 61.11% of modified lines in pull request are covered.

Additional details and impacted files

@@ Coverage Diff @@## main #188 +/- ##
==========================================
- Coverage 80.63% 80.06% -0.57% 
==========================================
Files 17 17 Lines 888 898 +10 ==========================================
+ Hits 716 719 +3 - Misses 172 179 +7 

Impacted Files	Coverage Δ
barcode/codex.py	80.31% <58.82%> (-2.93%)	⬇️
barcode/__init__.py	96.00% <100.00%> (+0.08%)	⬆️

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