3410 more namespace standards for physics and engineering variables

[chris-ashe]

This pull request includes significant updates to the variable naming conventions in the documentation/proc-pages/development/standards.md file. The changes introduce a standardized scheme for naming variables based on their data type, system, description, and units. Additionally, specific prefixes for different types of variables are defined to improve readability and consistency.

Variable Naming Conventions:

• Introduced a new variable naming scheme: var = <data type>_<system>_<description>_<units>. For physics variables not belonging to a system, the scheme is var = <physics variable>_<description>.
• Defined prefixes for various types of variables, such as radii (r_), thicknesses (dr_), integer countable items (n_), number densities (nd_), areas (a_), volumes (vol_), lengths (len_), velocities (vel_), mass (m_), pressures (pres_), densities (den_), voltages (v_), resistances (res_), resistivity (rho_), currents (c_), inductances (h_), current densities (j_), powers (p_), energies (e_), temperatures (temp_), times (t_), magnetic field strengths (b_), frequencies (freq_), and angles (deg_ or rad_).

Updates to Existing Variables:

• Updated existing variable names to follow the new naming conventions. For example, plasma_current is now c_plasma, and mass_steel is now m_steel.## Description

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.80%. Comparing base (73d1488) to head (a384030).
Report is 6 commits behind head on main.

Additional details and impacted files

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+ Coverage   28.27%   29.80%   +1.53%     
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  Files          77       77              
  Lines       18428    20836    +2408     
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+ Hits         5210     6211    +1001     
- Misses      13218    14625    +1407     

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[jonmaddock]

Looks great Chris, thanks for doing this.