molssi-seamm/read_structure_step: Added support for ASE style .extxyz files.

This PR adds support for ASE (Atomic Simulation Environment) style extended XYZ files (.extxyz) with appropriate unit handling (eV, Å, and time = Å*amu^0.5/eV^0.5). The changes also introduce file appending capabilities and support for reading compressed (bz2) SDF files.

Key changes:

• Added complete .extxyz format reader and writer with ASE compatibility
• Added append mode option for file writers where applicable
• Added extra_attributes parameter for .extxyz files to include custom metadata
• Updated multiple file format handlers to support the new append functionality