Issue 13/remove parquet extension check

[jacopoprandelli]

Remove file extension validation for Parquet files

Summary

Removes the requirement for files to have a .parquet extension. The application now validates files based on their actual content rather than their file extension.

Changes

• CLI: Removed file extension check - now accepts any file path
• ParquetReader: Enhanced validation to check file existence and let PyArrow validate the actual Parquet format
• Tests: Updated and added tests to cover:
  • Files without .parquet extension -> test_reader_accepts_file_without_parquet_extension
  • Invalid (non-Parquet) files -> test_reader_invalid_parquet_file
  • File not found errors -> test_reader_nonexistent_file

Closes #13

[raulcd]

This looks great, thanks for the PR!