Conjecture: No finite superstable Game of Life configuration exists

### What is the conjecture?

> A finite configuration is superstable if it can survive in any environment, no matter how hostile, meaning that if it should ever appear on the board, then it will definitely reappear later in exactly that same position, regardless of what else is happening on the board.

https://mathoverflow.net/questions/132687/is-there-any-superstable-configuration-in-the-game-of-life

### Prerequisites needed
Formalization of Game of Life dynamics

### [AMS categories](https://github.com/google-deepmind/formal-conjectures/labels?q=ams-)

(not sure)

### Choose either option
- [ ] I plan on adding this conjecture to the repository
- [x] This issue is up for grabs: I would like to see this conjecture added by somebody else

Start with the linked MathOverflow discussion and the repository's existing formalizations of Game of Life dynamics. Formalize the stated superstable-configuration conjecture in Lean; done means the conjecture has been added to the repository in an appropriate formal statement.

Written by the indexing model from the issue text.