Ed25519: remove v4.x CSK/HMAC; port and refactor (part three)

* stop generating and distributing the shared key
  - drop the CSK `revs` from metasync and the related metasync Tx/Rx
* control-plane port (`signIntra`/`verifyIntra`)
  - ported but not enabled yet (TODO)
* `nonce` (global) is now part of common `htrun`, alongside signing key pair
* rename across the board: "csk" => "sv", etc. etc.
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* prev. commits:
  - 501112a "lifecycle, persistence, cluster map, 5.0 bridge"
  - 1339a81 "httpclupost v5.0-bridge admission"

Signed-off-by: Alex Aizman <alex.aizman@gmail.com>

Author: alex-aizman