feat: Coding Theory, Gilbert Varshamov

[wurtylex]

We ported the majority of the code from https://github.com/wurtylex/LeanECC/tree/main.

We provide a basis for starting coding theory in cslib by providing formalization of

• Basic code and code properties.
• Hammingballs.
• Gilbert Varshamov bounds.

AI Statement

Todo..

Other Todos

• Follow Doc Header mathlib
• Follow PR title for commit convention.
• Take one final cleanup look

[ctchou]

I know this is still a draft, but I have two suggestions:

• Please add the reference to references.bib and refer to it like in a paper.
• Please split into 2 or 3 PRs to facilitate digestion by the reviewers.