Historical accounts state certificate processing

[whankinsiv]

This PR implements the placeholder handle_tx_certificates function to process and store historical registration, delegation, and MIR history by stake address. It contributes toward #256 and adds state support for:

• /accounts/{stake_address}/registrations
• /accounts/{stake_address}/delegations
• /accounts/{stake_address}/mirs

Main changes:

• Expanded certificate messages to {Type}WithPos wrappers in tx_unpacker to include TxIdentifier for historical tracking.
• Implemented handle_tx_certificates, which now processes all relevant certificate types via helper methods (handle_stake_registration_change, handle_stake_delegation, and handle_mir).
• Added get_registration_history, get_delegation_history, and get_mir_history to HistoricalAccountsState for aggregated retrieval from both volatile and immutable state.
• Added query handlers for GetAccountRegistrationHistory, GetAccountDelegationHistory, and GetAccountMIRHistory.

Next steps:

• A follow up PR will extend the rest_blockfrost module with REST handlers for the 3 endpoints listed above.

[sandtreader]

I wonder if rather than having all these xxxWithPos structs, we should generalise the TxCertificatesMessage to include them - e.g.

(types.rs)

pub struct TxCertificateWithPos {
   pub cert: TxCertificate,
   pub tx_identifier: TxIdentifier,
   pub cert_index: u64
}

(messages.rs)

pub struct TxCertificatesMessage {
    /// Ordered set of certificates
    pub certificates: Vec<TxCertificateWithPos>,
}

It saves all the extra structs and I think would make handling easier (at least, fewer changes to the original, although more to revert, sorry!)