[minibatch] Create minibatch from encoding streamer

[ian-shim]

Why are these changes needed?

Tweaks existing CreateBatch method that returns a minibatch.
CreateMinibatch method is equivalent to CreateBatch except:

• it removes the encoded blobs immediately once retrieved to make a batch
• it does not reset the reference block number

It also adds a UpdateReferenceBlock method that batch confirmer can call to reset the reference block number.

Checks

• I've made sure the lint is passing in this PR.
• I've made sure the tests are passing. Note that there might be a few flaky tests, in that case, please comment that they are not relevant.
• Testing Strategy
  • Unit tests
  • Integration tests
  • This PR is not tested :(