feat: Create hello world template with to_snake_case function

[matapatos]

Summary

• Created hello world template from validation-ext repository
• Added to_snake_case string conversion function
• Removed hello_world and pascal_triangle functions
• Added comprehensive C unit tests using TEST_CASE and TEST_MATRIX macros
• Included PHP integration tests with PestPHP
• Preserved Taskfile, Ceedling, and PestPHP configurations
• Updated minimum PHP version to 8.1

Files Changed

• template_ext.c - Main extension source with to_snake() function
• template_ext.h - Header file with function declarations
• config.m4 - PHP extension configuration
• composer.json - Updated PHP requirement to ^8.1
• Taskfile.yml - Task runner configuration
• project.yml - Ceedling test configuration
• tests/c/test_to_snake.c - C unit tests with TEST_CASE and TEST_MATRIX
• tests/c/support/test_helpers.c - Test helper functions
• tests/c/support/test_helpers.h - Test helper headers
• tests/php/Integration/ToSnakeTest.php - PHP integration tests
• tests/php/Pest.php - PestPHP bootstrap
• stubs/functions.stub.php - PHP function stubs
• README.md - Updated documentation

Testing

• C unit tests verify to_snake_case conversion including:
  • camelCase to snake_case
  • PascalCase to snake_case
  • kebab-case to snake_case
  • Space separated to snake_case
  • Edge cases (empty string, single char, all uppercase, all lowercase)
  • Numbers in strings
  • Multiple separators
  • Leading/trailing separators
  • Consecutive uppercase letters
  • Parameterized tests using TEST_MATRIX
• PHP integration tests verify extension functions work correctly

Closes #1