More or less a verbatim copy-paste minus some edgy variable naming and
internal `piker` module imports. There is a bunch of OHLC related
defaults that need to be dropped and we need to adjust to an optional
dependence on `numpy` by supporting shared lists as per the mp docs.

First attempt at getting `multiprocessing.shared_memory.ShareableList`
working; we wrap the stdlib type with a readonly attr and a `.key` for
cross-actor lookup. Also, rename all `numpy` specific routines to have
a `ndarray` suffix in the func names.

Demonstrates fixed size frame-oriented reads by the child where the
parent only transmits a "read" stream msg on "frame fill events" such
that the child incrementally reads the shm list data (much like in
a real-time-buffered streaming system).

Only found this by luck more or less (while working on something in
a client project) and it turns out we can actually get to (yet another)
hang state where SIGINT will be ignored by the root actor on teardown..

I've added all the necessary logic flags to reproduce. We obviously need
a follow up bug issue and a test suite to replicate!

It appears as though the following are required based on very light
tinkering:
- infected asyncio mode active
- debug mode active
- the `trio` context must breakpoint *before* `.started()`-ing
- the `asyncio` must **not** error

This works now for supporting a new `tractor.pause_from_sync()`
`tractor`-aware-replacement for `Pdb.set_trace()` from sync functions
which are also scheduled from our runtime. Uses `greenback` to do all
the magic of scheduling the bg `tractor._debug._pause()` task and
engaging the normal TTY locking machinery triggered by `await
tractor.breakpoint()`

Further this starts some public API renaming, making a switch to
`tractor.pause()` from `.breakpoint()` which IMO much better expresses
the semantics of the runtime intervention required to suffice
multi-process "breakpointing"; it also is an alternate name for the same
in computer science more generally: https://en.wikipedia.org/wiki/Breakpoint
It also avoids using the same name as the `breakpoint()` built-in which
is important since there **is alot more going on** when you call our
equivalent API.

Deats of that:
- add deprecation warning for `tractor.breakpoint()`
- add `tractor.pause()` and a shorthand, easier-to-type, alias `.pp()`
  for "pause-point" B)
- add `pause_from_sync()` as the new `breakpoint()`-from-sync-function
  hack which does all the `greenback` stuff for the user.

Still TODO:
- figure out where in the runtime and when to call
  `greenback.ensure_portal()`.
- fix the frame selection issue where
  `trio._core._ki._ki_protection_decorator:wrapper` seems to be always
  shown on REPL start as the selected frame..

For whatever reason pdb(p), and in general, will show the frame of the
*next* python instruction/LOC on initial entry (at least using
`.set_trace()`), as such remove the `try/finally` block in the sync
code entrypoint `.pause_from_sync()`, and also since doesn't seem like
we really need it anyway.

Further, and to this end:
- enable hidden frames support in our default config.
- fix/drop/mask all the frame ref-ing/mangling we had prior since it's no
  longer needed as well as manual `Lock` releasing which seems to work
  already by having the `greenback` spawned task do it's normal thing?
- move to no `Union` type annots.
- hide all frames that can add "this is the runtime confusion" to
  traces.

Detect if the input ref is a non-func (like an `object` instance) in
which case grab its type name using `type()`. Wrap all the name-getting
into a new `_mk_fqpn()` static meth: gets the "fully qualified path
name" and returns path and name in tuple; port other methds to use it.
Refine and update the docs B)