Fix: syntax errors in utility function validations

[abhayrajjais01]

Description

This PR addresses bugs in src/deepforest/utilities.py where validation checks would either crash the program or execute incorrect string length logic.

Changes:

• Deprecation Warnings: Replaced raise DeprecationWarning(...) with warnings.warn(..., DeprecationWarning). The previous implementation threw an exception and killed the process, effectively making the functions unreachable.
• String Length Check: Fixed a logic bug in __assign_image_path__ where len() was evaluated on the first character of the image path string instead of on the array of unique existing paths. This prevented false-positive warnings from firing on valid string paths.

Type of change

• Bug fix (non-breaking change which fixes an issue)
  nge which fixes an issue)

AI-Assisted Development

• I used AI tools (e.g., GitHub Copilot, ChatGPT, etc.) in developing this PR
• I understand all the code I'm submitting
• I have reviewed and validated all AI-generated code

AI tools used (if applicable):

AI tools were initially used to understand the codebase better. but code was written and verified manually.

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.65%. Comparing base (efb872f) to head (f6427b8).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/deepforest/utilities.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1336      +/-   ##
==========================================
+ Coverage   87.34%   87.65%   +0.31%     
==========================================
  Files          24       24              
  Lines        2978     2989      +11     
==========================================
+ Hits         2601     2620      +19     
+ Misses        377      369       -8     

Flag	Coverage Δ
unittests	87.65% <91.66%> (+0.31%)	⬆️

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[henrykironde]

Hi @abhayrajjais01, thanks for the suggestions. Could you share the script you were running when you encountered this bug? If you discovered it using AI, that’s also okay. Once I have that information, I can better guide you on how to proceed.

[abhayrajjais01]

Hi @henrykironde, thanks for reviewing!
Yes, I discovered these bugs through an AI, here is the context for each fix:

the original code used raise DeprecationWarning(...), which throws an exception and immediately terminates the function — making lines 231–236 unreachable dead code, any caller of shapefile_to_annotations() would always get a crash instead of the intended deprecation notice. the fix changes it to warnings.warn(..., DeprecationWarning) so the function actually completes and returns a result
In __assign_image_path__, the check len(existing_image_path) > 1 was called on a single path string, meaning the "multiple image paths" warning fired spuriously on virtually every call the fix changes the condition to check len(existing_image_paths) (the array of unique paths), which correctly warns only when there are actually multiple distinct image paths
let me know if you would like any other changes

[henrykironde]

If you take the time to fully understand the function, what it does, and how it is used, you may arrive at a good design or solution for this PR. I strongly encourage reviewing and understanding the code before submitting changes, rather than sending AI generated patches that may not yet be fully understood.

[henrykironde]

Please refer to the comment above