activator: move multicast group cleanup from CLI to activator

[snormore]

Summary of Changes

• Move multicast group unsubscribe responsibility from the SDK DeleteUserCommand to the activator's Deleting/PendingBan handlers, eliminating transitory onchain states that caused unnecessary daemon reconciler re-provisioning
• Allow onchain DeleteUser to proceed with non-empty publisher/subscriber lists (activator handles cleanup server-side before CloseAccount/Ban)
• Permit SubscribeMulticastGroup for users in Deleting status so the activator can unsubscribe them

Diff Breakdown

Category	Files	Lines (+/-)	Net
Core logic	4	+65 / -57	+8
Tests	2	+16 / -346	-330

Net deletion of ~320 lines, removing client-side retry/polling complexity in favor of server-side cleanup.

Key files (click to expand)

• activator/src/process/user.rs — add unsubscribe_all_multicast_groups() helper, call it in both stateful and stateless Deleting/PendingBan handlers before CloseAccount/Ban
• smartcontract/sdk/rs/src/commands/user/delete.rs — remove client-side unsubscribe loop, retry/polling logic, and associated imports; simplify tests
• smartcontract/programs/doublezero-serviceability/src/processors/multicastgroup/subscribe.rs — add Deleting to allowed user statuses for subscribe/unsubscribe
• smartcontract/programs/doublezero-serviceability/src/processors/user/delete.rs — remove ReferenceCountNotZero check blocking delete with non-empty groups
• smartcontract/sdk/rs/src/commands/multicastgroup/subscribe.rs — allow SDK subscribe command for Deleting users
• smartcontract/sdk/rs/src/commands/tenant/delete.rs — update cascade delete test to match simplified DeleteUserCommand

Deployment Order

These changes are backward-compatible if deployed in order:

1. Onchain program — deployed first so activator can unsubscribe Deleting users
2. Activator — picks up group cleanup responsibility
3. SDK/CLI — removes client-side unsubscribe loop

Testing Verification

• cargo test -p doublezero-serviceability — all 6 onchain program tests pass
• cargo test -p doublezero_sdk — all SDK tests pass including new test_delete_user_sends_delete_transaction_directly and updated test_delete_tenant_with_cascade
• make rust-lint — no clippy warnings
• Verified new test confirms DeleteUserCommand sends the delete transaction directly without any preceding unsubscribe transactions, even when user has non-empty publisher/subscriber lists