Complete TxStatusManager Service tests

[MitchTurner]

Implement the missing tests:

// Tests to implement
// 1. `status_update()` sends correct notifications for `tx_status_change` and
//    `new_tx_notification_sender` depending on the `TransactionStatus` variant.
// 2. `status_update()` updates the `statuses` map with the correct `TransactionStatus`.
//     for example `status_update()` does not update the `statuses` map
//     with the `TransactionStatus::SqueezedOut` (if we decide so)
// 3. Pruning of old statuses
//    - upon storage in DB
//    - other pruning scenarios if we decide to implement them
// 4. `status_update()` is called from all components: TxPool, Consensus, WorkerService and P2P
// 5. Signature is verified before the preconfirmations are accepted

[rafal-ch]

// 1. `status_update()` sends correct notifications for `tx_status_change` and
//    `new_tx_notification_sender` depending on the `TransactionStatus` variant.

tx_status_change is now covered with tests, new_tx_notification_sender is no longer a thing in TxStatusManager (it's handled by TxPool)

---

// 2. `status_update()` updates the `statuses` map with the correct `TransactionStatus`.
//     for example `status_update()` does not update the `statuses` map
//     with the `TransactionStatus::SqueezedOut` (if we decide so)

In the current implementation the status_update() function does not have any logic whether to update the status or not - it always updates the status to whichever status was received and this behavior is already covered with tests

---

// 3. Pruning of old statuses
//    - upon storage in DB
//    - other pruning scenarios if we decide to implement them

Pruning of old statuses is purely TTL based. There is a notion of prunable and non-prunable statuses and the pruning behavior is already covered with tests.

---

// 4. `status_update()` is called from all components: TxPool, Consensus, WorkerService and P2P

Added tests covering interactions between TxPool and TxStatusManager. There are 2 TODOs left to cover Consensus and WorkerService, and P2P has no direct interaction with TxStatusManager.

---

// 5. Signature is verified before the preconfirmations are accepted

This behavior is already covered with tests.

[rafal-ch]

In addition to what's in the description some more coverage has been added in the linked PR.