vyzo's review of the dagstore

[vyzo]

Haven't dived into the subdirectories yet.

[vyzo]

So far one minor bug (see comments inline) and one recommendation for refactoring:
The task processing logic of the event loop should be extracted on its own method, which can then:

• lock/defer unlock to avoid having a really long lock scope with a bunch of pasta in-between
• return the next task and avoid the internaclCh indirection, which can now be removed altogether.