Recognize lg as an ASCIIMath function

[luantaraschi]

Fixes #522

Summary

Add lg to the ASCIIMath function-name list so it is spaced as a function rather than treated as a generic identifier. The change also adds an Augenbit regression test for lg a.

Verification

• Before the rule change, the regression produced an unspaced identifier form instead of lg a.
• The full Braille suite passes with 1,694 tests passed, 35 ignored, and no failures.
• uv run pytest passes with 88 tests.

[NSoiffer]

Thanks for the fix and test.