feat(dataset): make image extension matching case-insensitive

[veezhang]

Pull Request Template

Checklist

• Confirmed that cargo run-checks command has been executed.
• Made sure the book is up to date with changes in this PR.

Related Issues/PRs

Provide links to relevant issues and dependent PRs.

Changes

Image file extensions should be case-insensitive.
For example, ImageNet uses the .JPEG extension.

Testing

cargo test -p burn-dataset image_folder_dataset --features vision                                                                                                                             ─╯
   Compiling burn-dataset v0.22.0-pre.1 (/repo/github/veezhang/burn/crates/burn-dataset)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 1.45s
     Running unittests src/lib.rs (target/debug/deps/burn_dataset-c503b61fdf267fca)

running 6 tests
test vision::image_folder::tests::image_folder_dataset_invalid_extension - should panic ... ok
test vision::image_folder::tests::image_folder_dataset_with_items ... ok
test vision::image_folder::tests::image_folder_dataset_multilabel ... ok
test vision::image_folder::tests::image_folder_dataset_filtered ... ok
test vision::image_folder::tests::image_folder_dataset ... ok
test vision::image_folder::tests::image_folder_dataset_with_items_sizes ... ok

test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured; 59 filtered out; finished in 0.00s

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.93%. Comparing base (2b70b67) to head (f9057ba).
⚠️ Report is 11 commits behind head on main.

❌ Your project check has failed because the head coverage (65.93%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5152      +/-   ##
==========================================
- Coverage   65.98%   65.93%   -0.05%     
==========================================
  Files        1191     1194       +3     
  Lines      181679   182149     +470     
==========================================
+ Hits       119874   120107     +233     
- Misses      61805    62042     +237     

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