air: domain-separate bus messages by interaction namespace, not by bus type

Follow-up from #2856.

After the bus-prefix refactor, we domain-separate per `bus_type` (e.g. `CHIPLETS_BUS`), but logically distinct cancelable message families share one prefix and still rely on op-labels encoded into the message body for disambiguation.

Proposal: assign one prefix per *balancing interaction namespace* (memory element, memory word, hasher permutation link, ACE read, ACE eval, range-check, decoder→stack overflow, etc.) instead of per bus column. Benefits:

- Most of the current op-label machinery becomes redundant and can be dropped.
- Cross-family denominator collisions become impossible by construction, not by label convention.
- Simplifies reasoning about bus-message uniqueness.

May be executed alongside the LogUp refactor (#2962) — flagging for scoping.

_Originally posted by @Al-Kindi-0 in https://github.com/0xMiden/miden-vm/pull/2856#discussion_r3089158554 and @adr1anh in https://github.com/0xMiden/miden-vm/pull/2856#discussion_r3092560703_