feat: historical accounts reward processing

[whankinsiv]

This PR implements reward processing in historical_accounts_state and adds the /accounts/{stake_address}/rewards REST handler in rest_blockfrost as part of #256.

Main changes:

• Refactored StakeRewardDeltasMessage to exclude MIR reward deltas.
• Expanded StakeRewardDelta to include reward type and pool information.
• Updated accounts_state to credit MIRs immediately instead of at epoch transition, preventing balance underflow when users withdraw rewards early.
• Implemented handle_rewards, get_reward_history, and GetAccountRewardHistory query handler in historical_accounts_state.
• Added and registered the /accounts/{stake_address}/rewards endpoint via handle_account_rewards_blockfrost.

Next steps:

• A follow up PR will implement address deltas processing in historical_accounts_state and the corresponding /accounts/{stake_address}/addresses REST endpoint.