Move scheme to allow measurers to skip cell *cryption most of the time
to an appendix; in the short term measurers will verify all cells.

Signed-off-by: David Goulet <dgoulet@torproject.org>

Our docs accurately describe how to remove MAPADDRESS entries, but doesn't
demonstrate it. Exemplifying how to query our mappings and remove them.

  tpo/core/tor#40104

(tjr is okay with this)

It's under discussion on tor-dev.

We've talked about these, and in some cases begun to implement them.

They are implemented, and only need (possible) spec updates

Closes #30123