Add tests for code download pages for Belyi maps

[rvisser7]

This PR just adds some code testing for the code downloads for the Belyi maps pages. The snippet log files for Sage and Magma are included.

As always, feedback/comments welcome!

[roed314]

Again, GPT has some helpful suggestions: https://chatgpt.com/share/6a6eb147-fd04-83ea-8b6a-c267ce40ad79

[rvisser7]

Thanks, these GPT reviews are very useful! Here are the new changes:

• Added a test for the genus 2 case 7T5-7_7_3.3.1-a and a test where the transitive group number has two digits 6T15-5.1_5.1_5.1-c (these are also tested in the CI in test_belyi.py file)
• Fixed the Sage bugs for constructing the elliptic curve over the base field K, and the transitive group index parsing (also tested in test_belyi.py).