Fix layer ID determination to use only the first group of contiguous digit

[abey79]

Description

This address WTF cases like 01-layer1 ending in layer 11, but does not address cases like both green1 and blue1 ending in layer 1 (#594). This would require use the AxiDraw semantic (layer ID must be the first non-whitespace character), but would break situation like layer 1 and layer 3.

Checklist

• feature/fix implemented
• code formatting ok (black and isort)
• mypy returns no error
• tests added/updated and pytest succeeds
• documentation added/updated
  • command docstring and option/argument help
  • README.md updated (Feature Overview)
  • CHANGELOG.md updated
  • added new command to reference.rst
  • RTD doc updated and building with no error (make clean && make html in docs/)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (292f1b3) 94.74% compared to head (85d063f) 94.76%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #606      +/-   ##
==========================================
+ Coverage   94.74%   94.76%   +0.01%     
==========================================
  Files          62       62              
  Lines        5690     5710      +20     
  Branches     1302     1304       +2     
==========================================
+ Hits         5391     5411      +20     
  Misses        182      182              
  Partials      117      117              

Impacted Files	Coverage Δ
vpype_cli/read.py	96.22% <ø> (ø)
tests/test_files.py	98.63% <100.00%> (+0.09%)	⬆️
vpype/io.py	85.27% <100.00%> (+0.21%)	⬆️

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