Add stylistic variant for the italic "f" in Monaspace Neon

Hi, I'd like to request a new glyph variant for the italic lowercase "f" in the Monaspace Neon family, specifically, one with an extended terminal that reaches further downward (like Monaspace Argon, with longer tail). Thanks too much for your consideration.

Compare the italic lowercase "f" in the Monaspace Neon and Monaspace Argon families, focusing on the requested terminal and longer tail. Find the font source and build or preview workflow for glyph variants. Done means Monaspace Neon includes the requested stylistic variant and its generated font output can be verified.

Written by the indexing model from the issue text.