Support greek lambda character

First off, thanks for this great package! I'm not sure if this would qualify as a bug or a feature, but it would be great to get access to the $\lambda$ character using latexify.

Environment

• OS: Ubuntu 24.04
• Python: 3.12
• Package manager: pip 24.2.1
• Latexify version: latest (https://github.com/google/latexify_py/commit/54dc8697196370dad227b0d516b42f6b82825852)

Description

I would like to use the $\lambda$ symbol in my formulas but currently that raises an error.

Reproduction

import latexify

@latexify.function(identifiers={"foo": "f", "lambda_": "lambda"}, use_math_symbols=True)
def foo(lambda_):
    return lambda_ + 1

foo

This gives me a `ValueError: 'lambda' is not an identifier name.`.

Expected behavior

I would expect to be allowed to use the lambda symbol in LaTeX.

If I comment out these two lines, e.g. it does not throw an error when lambda is used. Obviously those line are probably there for a reason, so I'm not sure what the consequences are when they are removed, but perhaps the restrictions on the value side of the identifiers could be a bit more lenient...?

https://github.com/google/latexify_py/blob/54dc8697196370dad227b0d516b42f6b82825852/src/latexify/transformers/identifier_replacer.py#L42-L43

Screenshot of the output when those lines are commented out.