Mostly adjustments for the new pld-receiver semantics/shim-layer which
results more often in the direct delivery of `RemoteActorError`s from
IPC API primitives (like `Portal.result()`) instead of being embedded in
an `ExceptionGroup` bundled from an embedded nursery.
Tossed usage of the `debug_mode: bool` fixture to a couple problematic
tests while i was working on them.
Also includes detailed assertion updates to the inter-peer cancellation
suite in terms of,
- `Context.canceller` state correctly matching the true src actor when
expecting a ctxc.
- any rxed `ContextCancelled` should instance match the `Context._local/remote_error`
as should the `.msgdata` and `._ipc_msg`.
683288c8db