Implement MockDaService

[bkolad]

Background

To test a complete transaction processing workflow, we need to initiate a celesta service in an external docker container. As a result, we are unable to execute self-contained E2E unit tests for the rollup. To address this limitation, we should create a MockDaService that stores transaction blobs in memory. This will allow us to perform tests without relying on the external service.

Proposed solution:

• 1. Extract the blob processing logic from demo-rollup. The logic should depend only on the DaService trait instead of a specific DA implementation. This abstract logic will reside in a separate crate (called rollup?), which will be responsible for "running" the rollup. Take a look at issue Move out custom rollup logic from demo-rollup and demo-prover  #459 for more details.
• 2. Implementdemo-rollup using (1). The main function of the demo-rollup should take a runtime, rollup and specific da service (celestial for now) and seamlessly integrate them with very little custom logic involved.
• 3. Implement the DaService trait for MockDaService. We can start from the following code.
• 4. Test (1) with the MockDaService
• 5. Use (1) & (3) for E2E tests for our runtime (including queries and send_transaction endpoints)

[bkolad]

For point 3 the MockDaService has to support at least the following methods:

let filtered_block = self.da_service.get_finalized_at(height).await?;
let mut blobs = self.da_service.extract_relevant_txs(&filtered_block);

Inside MockDaService we could keep a queue of pending blobs and index it by FileredBlock (TestBlock in MockDaService.)