[FIX] Gracefully handle user providing phenotypic file as .csv

[surchs]

Closes #90

Changes proposed in this pull request:

• raise errors if
  • user provides a file ending in .csv
  • user provides a .tsv file, that really is just a repackaged .csv file -> we're not fooled 👀

Checklist

• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see https://neurobagel.org/contributing/pull_requests for more info)
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions.

[github-actions]

Pull Request Test Coverage Report for Build 6316815673

• 36 of 36 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 99.678%

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Totals
Change from base Build 6314697288:	0.007%
Covered Lines:	1239
Relevant Lines:	1243

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💛 - Coveralls

[alyssadai]

Thanks @surchs for addressing this!

Everything seems good functionally, but I've left a few clarification questions and 🍒 comments below I think would be worth having another look at.

[alyssadai]

Two 🍒 suggestions, otherwise looks good to go!!