feat: support automatic language code determination with `guesslang`

[lh0x00]

Pull Request Description

Summary

This PR enhances _CustomMarkdownify with a feature:

1. Automatic Code Language Detection:
   • Uses guesslang to detect programming languages in code snippets.
   • Provides a fallback if guesslang is not installed.

Changes

• Imported Guess from guesslang with a fallback.
• Added code_language_callback to detect code languages.

How to Test

1. Install guesslang via pip install guesslang.
2. Convert a document with code snippets.
3. Verify correct language detection.

Thank you for reviewing!

[afourney]

Love this idea, but I'm thinking of using magika for type detection (See #1108). Since magika can do code language detection as well, would you consider updating this PR to use it instead (to avoid another dependency)?

You should be able to just do:

from magika import Magika
m = Magika()
res = m.identify_bytes(b".... contents of the code block ...")
if res.status == "ok" and res.prediction.output.group in ["text", "code"]:
    language =  res.prediction.output.label

Or something like that.

[lh0x00]

I rebase it with your magika branch, and update it as requested, it should be merged after magika. Thanks!