Feat: Add blockchain data structure

[hanibhat]

What

This PR adds a blockchain data structure implementation with blocks, transactions, mining, chain validation, balance lookup, and transaction history lookup.

Why

A blockchain is a useful applied example of several data structure ideas working together:

• A chain-like structure where each node points back to prior state.
• Hashing for integrity checks.
• Maps for efficient balance and transaction indexes.
• Queues/lists for pending transactions.

[Spaceplasma1976nasaAllenvbelt]

What

This PR adds a blockchain data structure implementation with blocks, transactions, mining, chain validation, balance lookup, and transaction history lookup.

Why

A blockchain is a useful applied example of several data structure ideas working together:

• A chain-like structure where each node points back to prior state.
• Hashing for integrity checks.
• Maps for efficient balance and transaction indexes.
• Queues/lists for pending transactions.

Block chain is where he put five people shares in Stocks and OM numbers beneficiary. They keep taking it out to steal it through bitcoin they reinstall it into the Edgar system with Pokémon cards that kids buy they all have Edgar numbers on it if you can scan them.