update to diffo 0.2.1

[matt-beanland]

incorporates ash_neo4j 0.4.1 and bolty 0.0.12, should properly support transactions and test sandbox.

convert tests to sandbox
handle dsl evolution (structure, behaviour)

[matt-beanland]

updated deps encountered known issue with over-verification of owner in party extension - fix deferred to /diffo-dev/diffo#101
DiffoExample.Nbn.Rsp is impacted.

[matt-beanland]

dsl evolution not required - party dsl hasn't yet evolved to structure/behaviour (and may not).

transactions are inherent

updated tests to use sandbox, needed to change application.ex since initialiser should only be called with cowboy for livebook, not for tests.

[matt-beanland]

changed tests to

Ex.Unit.Case, async: true 

for all test modules. With the sandbox binding the connection to the test process, concurrent tests get isolated Neo4j transactions and can't interfere with each other, since the sand-box is process bound.

Watch for anything that goes through a process that isn't a descendant of the test process (e.g., a Task.async or GenServer call inside the code under test). Those won't automatically inherit the sandbox connection — they'd need an explicit AshNeo4j.Sandbox.allow(test_pid, other_pid) call. Worth keeping in mind if you ever see intermittent DB-not-found errors in async mode with concurrent processes.

But for the current test suite as it stands, adding async: true to every module should work cleanly.