feat Added multiple improvements

[vamsikunal]

improvements to the blockchain's block structure, validation logic, and light node support, as well as updates to dependency management.

• Added SlotNumber to the Block struct to support deterministic block timing and updated block creation, serialization, and hash computation to include this field. Block validation now checks for strictly increasing slot numbers.

• Enhanced block validation to require all expected domain expirations (via expiryChecker) to be present in the block, enforcing strict checks on expiration transactions.

• Added BlockHeader and MerkleProof types, with methods for extracting lightweight block headers and generating/verifying compact Merkle proofs for transaction inclusion, enabling efficient light node operation.

• Introduced a new spent_txs bucket to the blockchain database for tracking spent transactions.

• Improved AddBlock logic to ensure chain tip is only updated if the new block properly extends the current chain, preventing index gaps and forks from incorrectly updating the tip.

---