Since it's going to be used from the IPC primitive APIs
(`Context`/`MsgStream`) for similarly handling payload type spec
validation errors and bc it's really not well situation in the IPC
module XD
Summary of (impl) tweaks:
- obvi move `_mk_msg_type_err()` and import and use it in `._ipc`; ends
up avoiding a lot of ad-hoc imports we had from `._exceptions` anyway!
- mask out "new codec" runtime log emission from `MsgpackTCPStream`.
- allow passing a (coming in next commit) `codec: MsgDec` (message
decoder) which supports the same required `.pld_spec_str: str` attr.
- for send side logging use existing `MsgCodec..pformat_msg_spec()`.
- rename `_raise_from_no_key_in_msg()` to the now more appropriate
`_raise_from_unexpected_msg()`, but leaving alias for now.
baee808654