feat: Tests for invalid data in GTFS dataset

[CBROWN-ONS]

Description

closes #66

This PR provides testing for cases where invalid data has been introduced into the GTFS tables. This includes invalid and non-matching IDs. The tests ensure that these cases are identified and relayed back to the user through gtfs_kit.feed.validate() or in this case GtfsInstance().is_valid().

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

Test configuration details:

• OS: Windows 10
• Python version: 3.9.13
• Java version: N/A
• Python management system: conda

Checklist:

• My code follows the intended structure of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (87216ed) 87.27% compared to head (e847951) 87.27%.
Report is 16 commits behind head on dev.

Additional details and impacted files

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  Coverage   87.27%   87.27%           
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  Files          11       11           
  Lines         896      896           
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  Hits          782      782           
  Misses        114      114           

Flag	Coverage Δ
unittests	87.27% <ø> (ø)

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[r-leyshon]

@CBROWN-ONS please see comments in PR. Happy to have a call if anything is unclear, let me know.