fleet: busbar pin -> predev 163843dd2c59; tests at the pin's contract

[MattJackson]

Moves busbar-store-memory to busbar predev 163843dd2c59cd5a1181bdeed078f75dc6bdef97 (1.6.0), /status rows 81 and 136.

• The fleet template is rendered by busbar-release main 9b8327b06b95 (plugin render --tree . --pin 163843dd2c59 1.6.0), the same renderer plugin-drift runs; Cargo.lock is re-seeded from busbar's lock at the pin (lock parity) and the manifests' busbar revs move with .busbar-ref.
• The plugin's tests are moved to the contract at that pin (see the commits). No behaviour of the plugin changes.

Supersedes the drift sync PR's pin (7356bbfb6b) for this repo.

[MattJackson]

Superseded: the drift sync PR #10 (busbar-release main 1b722918, busbar predev 1d37d863a9) is green and merged into dev; this repo needed no code change at the pin (the suite's STORE_OPID_CONFLICT was the old suite's shared op-id mint, fixed in busbar at the pin).