feat(client): add chain spec api

[sinzii]

Unified chain spec api for both v2 and legacy client, we removed the method to fetch genesis hash since it's already fetched and available within the client during initialization.

const client = await DedotClient.new({ ... });

console.log('chain genesisHash', client.genesisHash);
console.log('chain name', await client.chainSpec.chainName());
console.log('chain props', await client.chainSpec.properties());