Improve Python syntax highlighting

[chbk]

Release Notes:

• Improved Python syntax highlighting.

Zed 0.174.6	With this PR

• identifier: variable
• ., ,, :: punctuation.delimiter
• @: operator, for matrix multiplication

class Mat(list):
  def __matmul__(self, b):
    ...
a, b = Mat(), Mat()
identifier = a @ b
IDENTIFIER = True

[maxdeviant]

Thanks!