minor: Add "msg" and "op" to hidden inlay parameter names

[joe-p]

"msg" adds noise to expect and crossbeam's Sender. "op" adds noise to map_err. There's probably more instance of each, but I noticed these all in one snippet:

[ChayimFriedman2]

I'm not enthusiast to add new names to the exclusion. op is pretty generic, and also used in the standard library, so I guess it is fine. However msg could provide extra information plus it's not used in std, as such I'd prefer not to add it.

[joe-p]

However msg could provide extra information plus it's not used in std, as such I'd prefer not to add it.

msg is used by core::result::Result::expect. Since these are only hidden for unary functions I personally think msg is along the same lines as value in terms of significance.

That being said, if the consensus is to just have op I can make that change, but wanted to make the case for msg

[ChayimFriedman2]

Makes sense.

Thanks!