* op-batcher: Prepare multi-frame support

* op-batcher: adapt tests to multi-frame txData

* op-batcher: add multi-blob transaction support

The existing configuration parameter TargetNumFrames can be used to specify
the desired number of blobs per transaction.

* op-batcher: improve blobs configuration (for testing)

* op-e2e: add multi-blob batcher test

* op-batcher: consolidate txID String & TerminalString impls

and add a test for it.

* op-batcher: Fix config test

* op-e2e: Improve multi-blob test to assert full blobs

* op-batcher: resolve open TODOs & renames (multi-blob)

* op-batcher: Test channel.NextTxData for single and multi frame txs