Readability improvements

[guzzijones]

Readability-only cleanup pass across the conductor, graph, spec, state-machine
and event layers. These changes make the code easier to follow without
altering any design decision, runtime behavior, or the serialized wire format
that StackStorm persists to Mongo. Specifically:

• Documented the previously implicit data shapes as type aliases and
  TypedDict/NamedTuple definitions in statetypes.py (RouteId vs
  RouteDetails/RoutesRegistry, TaskTransition, TaskId,
  transition-id conventions), and added module/class/method docstrings and
  annotations to events.py and machines.py explaining the two state
  machines and their current status -> {event name -> new status} tables.
• Replaced magic positional indexes on workflow-graph edges with a
  TaskTransition named tuple, so the conductor and graph read
  t.source / t.destination / t.key / t.data instead of
  t[0..3]. TaskTransition is a tuple subclass, so positional
  access, unpacking, sorting and set-dedup are unchanged. Likewise
  extract_vars now returns a ContextVar named tuple.
• Named the recurring literal 0 used for the root context/route as
  constants.ROOT_CONTEXT_INDEX / ROOT_ROUTE_ID, and the implicit retry
  attempt count as DEFAULT_RETRY_COUNT.
• Added a dictionary.first_item helper for the single-key-dict spec case,
  and switched (errors, ctx) result handling to named unpacking.
• No copies added or removed: every json_util.deepcopy call site is
  unchanged, and all shared payloads (context dicts, action dicts, edge
  data dicts) remain the same references they were before — preserving the
  deliberate no-copy coupling with StackStorm. The changes are allocation
  neutral: the spec-rendering paths allocate slightly less (first_item
  avoids materializing list(dict.items()); a redundant one-element slice
  was removed), offsetting the one extra wrapper tuple per graph edge, whose
  inner data dict is never copied. All 865 unit tests pass unchanged.
• Removed the standalone mock test dependency in favor of the stdlib
  unittest.mock.

[guzzijones]

3.10 is missing some of the features i use. I will circle back later and fix those.