Fix CalculateSHA256 function to validate file type

[mattdot]

This pull request includes several changes aimed at improving file hashing, adding commit message instructions, and enhancing testing. The most important changes are grouped into improvements to file hashing, commit message instructions, and testing.

Improvements to file hashing:

• internal/helpers/hash.go: Added checks to ensure the file is a regular file and not a symbolic link before attempting to calculate its SHA256 hash.

Commit message instructions:

• .github/copilot-commit-message-instructions.md: Added instructions to write commit messages conforming to the Convention Commits 1.0.0 specification.
• .vscode/settings.json: Updated settings to include the path to the commit message instructions file.

Testing enhancements:

• internal/helpers/hash_fuzz_test.go: Added a fuzz test for the CalculateSHA256 function to ensure it handles various edge cases and errors gracefully.

Additionally, a change log entry was added to document the improvement in file hashing:

• .changes/unreleased/fixed-20250411-043430.yaml: Documented the improvement in file hashing to check if a file is a real file and not a symbolic link.

[Copilot]

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Files not reviewed (1)

• .vscode/settings.json: Language not supported

Comments suppressed due to low confidence (2)

internal/helpers/hash.go:29

• [nitpick] Consider updating the error message to explicitly mention that symbolic links are not supported, so the user understands why the file is rejected.

if !fileInfo.Mode().IsRegular() {

internal/helpers/hash.go:25

• Ensure that the 'fmt' package is imported in this file since the error formatting relies on fmt.Errorf.

return "", fmt.Errorf("failed to stat file '%s': %w", filePath, err)