Use huge_tree=True in lxml parsing

[yrrepy]

Description

Enabled lxml support for very deep trees and very long text content in the geometry Python class. (huge_tree=true)

For large lattices with many elements (>~500,000 elements) the Python Universe plotter would fail due to the "huge text node". With this change I can successfully universe.py plot my highly detailed voxel lattice.

The change implemented follows that counselled here:
https://stackoverflow.com/questions/11850345/using-python-lxml-etree-for-huge-xml-files

Fixes:
The error appearing during universe.py plotting was:

Traceback (most recent call last):
  File "/home/abc/Projects/UniversePlotter.py", line 116, in <module>
    my_geometry=openmc.Geometry.from_xml();
  File "/home/abc/.local/lib/python3.10/site-packages/openmc/geometry.py", line 296, in from_xml
    tree = ET.parse(path)
  File "src/lxml/etree.pyx", line 3541, in lxml.etree.parse
  File "src/lxml/parser.pxi", line 1879, in lxml.etree._parseDocument
  File "src/lxml/parser.pxi", line 1905, in lxml.etree._parseDocumentFromURL
  File "src/lxml/parser.pxi", line 1808, in lxml.etree._parseDocFromFile
  File "src/lxml/parser.pxi", line 1180, in lxml.etree._BaseParser._parseDocFromFile
  File "src/lxml/parser.pxi", line 618, in lxml.etree._ParserContext._handleParseResultDoc
  File "src/lxml/parser.pxi", line 728, in lxml.etree._handleParseResult
  File "src/lxml/parser.pxi", line 657, in lxml.etree._raiseParseError
  File "geometry.xml", line 435
lxml.etree.XMLSyntaxError: xmlSAX2Characters: huge text node, line 435, column 10000881

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• 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)

[paulromano]

Thanks @yrrepy! Sorry for the delay on this one.