Use sync requests in inspector-*

[ckoparkar]

As discussed in #1807 (comment), the inspector-* fn's use callbacks to interact with the middleware. This PR changes those fn's to use the cider-sync-request:*.

• The commits are consistent with our contribution guidelines
• You've added tests (if possible) to cover your change(s)
• All tests are passing (make test)
• The new code is not generating bytecode or M-x checkdoc warnings
• You've updated the changelog (if adding/changing user-visible functionality)
• You've updated the readme (if adding/changing user-visible functionality)
• You've updated the refcard (if you made changes to the commands listed there)

Thanks!

[ckoparkar]

Probably we should change this name. But I couldn't think of anything better.

[bbatsov]

How about cider-inspector--render-value?

[ckoparkar]

Yep. I hadn't used that one because we already have a couple of render methods here :-) But that does seem to be the best one. Changed it now.