By borrowing from the implementation of `RemoteActorError.pformat()`
which is now factored into a new `.devx.pformat_exc()` and re-used for
both error types while maintaining the same func-sig. Obviously delegate
`RemoteActorError.pformat()` to the new helper accordingly and keeping
the prior `body` generation from `.devx.pformat_boxed_tb()` as before.
The new helper allows for,
- passing any of a `header|message|body: str` which are all combined in
that order in the final output.
- getting the `exc.message` as the default `message` part.
- generating an objecty-looking "type-name" header to be rendered by
default when `header` is not overridden.
- "first-line-of `message`" processing which we split-off and then
re-inject as a `f'<{type(exc).__name__}( {first} )>'` top line header.
- an optional `tail: str = '>'` to "close the object"-look only added
when `with_type_header: bool = True`.
Adjustments to `TransportClosed` around this include,
- replacing the init `cause` arg for a `src_exc` which is now always
assigned to a same named instance var.
- displaying that new `.src_exc` in the `body: str` arg to the
`.devx.pformat.pformat_exc()` call so you can always see the
underlying (normally `trio`) source error.
- just make it inherit from `Exception` not `trio.BrokenResourceError`
to avoid handlers catching `TransportClosed` as the former
particularly in testing when we want to sometimes to distinguish them.
Since `._code` is prolly gonna get renamed (to something "frame & stack
tools" related) and to give a bit better organization.
Also adds a new `add_div()` helper, factored out of ctxc message
creation in `._rpc._invoke()`, for adding a little "header line" divider
under a given `message: str` with a little math to center it.
Tyler Goodlet