Random Number Generator

[0xNeshi]

Issue(s): Close #128

Description

Built off of https://github.com/NethermindEth/StarknetByExample/pull/183

Explain randomness in the context of blockchain, and Starknet specifically, and provide an example with CoinFlip contract.

Checklist

• [x] CI Verifier: Run ./scripts/cairo_programs_verifier.sh successfully
• [x] Contract Tests: Added tests to cover the changes
• [x] Deployed Contract (Optional): If possible, include a Voyager link to a deployed contract on Sepolia
  • fund the contract with ETH if necessary:

[0xNeshi]

Converting to draft: fixing the fee refund logic

[0xNeshi]

Converting to draft: fixing the fee refund logic

In the end simplified the contract logic to make the example focus more on the randomness generation part.