Refactored Version of Electron Transport Capability

[melekderman]

❗ This PR is a refactor of #355 and closes #355. It should be merged after #383.

This pull request introduces foundational support for electron transport in the codebase, including new constants, data structures, and getter/setter modules for electron-related physics and tallying. The changes lay the groundwork for handling electron interactions in simulations, similar to existing neutron transport features.

The most important changes are:

Electron Physics Support and Constants

• Added new electron reaction types and a scoring type for energy deposition in mcdc/constant.py, as well as fundamental physical constants for electrons (mass, cutoff energy, fine structure constant, etc.). [1] [2] [3]
• Modified the simulation preparation logic in mcdc/main.py to initialize electron data for elements when electron transport is enabled.

Electron Data Structures and Accessors

• Introduced new getter and setter modules for electron reactions, elements, and related tallies in both mcdc_get and mcdc_set packages, including electron_reaction.py, electron_bremsstrahlung_reaction.py, electron_elastic_scattering_reaction.py, electron_excitation_reaction.py, electron_ionization_reaction.py, and element.py. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Native Material Extensions

• Added support for storing and accessing element IDs and densities in mcdc/mcdc_get/native_material.py, analogous to existing nuclide data. [1] [2]

Collision and Tally Infrastructure

• Added new getter and setter modules for collision data and collision tallies, supporting the new electron interactions. [1] [2] [3] [4] [5]

These changes establish the infrastructure needed for electron transport and tallying, bringing the codebase closer to supporting coupled neutron-electron physics.