Enable running a concrete test from a test file

[Chemaclass]

📚 Description

Enable running a concrete test by specifying the function name or line number directly in the file path, similar to how other testing frameworks (like PHPUnit or pytest) allow targeting specific tests.

This feature adds two new syntaxes:

• path::function_name - Filter tests by function name (supports partial matching)
• path:line_number - Run the test function that contains the specified line

🎯 Usage Examples

Run a specific test by function name

./bashunit tests/unit/example_test.sh::test_my_function

Run tests matching a partial name

# Runs all tests containing "spy" in their name
./bashunit tests/unit/test_doubles_test.sh::test_spy

Run the test at a specific line number

# Useful when jumping to a test from your editor
./bashunit tests/unit/example_test.sh:42

Error handling for invalid line numbers

# Shows error if line is before any test function
./bashunit tests/unit/example_test.sh:1
# Error: No test function found at line 1 in tests/unit/example_test.sh

Traditional filter still works

./bashunit tests/unit/example_test.sh --filter test_my_function

🔖 Changes

• Add helper::parse_file_path_filter() to extract filter from file path
• Add helper::find_function_at_line() to resolve line numbers to test functions
• Update main::cmd_test() to process inline filters from file paths
• Add unit tests for the new helper functions
• Add acceptance tests for end-to-end validation

🖼️ Doc

✅ Checklist

• I updated the CHANGELOG.md to reflect the new feature
• Tests pass locally
• Documentation updated

Closes #496