using library from endf package

[shimwell]

Description

Replaced the local _LIBRARY and _SUBLIBRARY dicts in
openmc/data/endf.py with a single import from endf.material.

• Key 21 corrected: 'SG-21' → 'SG-23' to match python-endf implementation
• Key 38 added: 'IAEA/PD' (was missing from OpenMC)

link to endf-python implementation https://github.com/paulromano/endf-python/blob/d39c040cf8685800dbe01c40f133e150f5df1426/src/endf/material.py#L41-L61

Fixes # (issue)

Checklist

• I have performed a self-review of my own code
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)