To handle captured non-egs (when the now optional `tn` isn't provided)
as well as yield up a `BoxedMaybeException` which contains any detected
and un-masked `exc_ctx` as its `.value`.
Also add some additional tooling,
- a `raise_unmasked: bool` toggle for when the caller just wants to
report the masked exc and not raise-it-in-place of the masker.
- `extra_note: str` which by default is tuned to the default
`unmask_from = (trio.Cancelled,)` but which can be used to deliver
custom exception msg content.
- `always_warn_on: tuple[BaseException]` which will always emit
a warning log of what would have been the raised-in-place-of
`ctx_exc`'s msg for special cases where you want to report
a masking case that might not be otherwise noticed by the runtime
(cough like a `Cancelled` masking another `Cancelled) but which
you'd still like to warn the caller about.
- factor out the masked-`ext_ctx` predicate logic into
a `find_masked_excs()` and also use it for non-eg cases.
Still maybe todo?
- rewrapping multiple masked sub-excs in an eg back into an eg? left in
#TODOs and a pause-point where applicable.
eddbedb97d