Function createImmediateConcurrency

Lighter-weight concurrency strategy that applies commits and intermediate steps immediately with no global rollback-and-replay cycle.

Key differences from createRebaseReplayConcurrency:

• No deferred-commit mode — db.transactions.X(args) commits synchronously with positive time.
• No global rebase: when an inbound committed envelope arrives, it is applied directly without rolling back other pending transients. This means entity-id allocation is NOT deterministic across peers under concurrent edits — use this only when there is a single writer or when an external layer manages replay (e.g. a collaborative-editing wrapper).
• Async generator intermediate steps are still supported: each yield applies the intermediate state immediately and rolls it back when the next yield or the final commit arrives. Cancel rolls back the last applied intermediate step for that transaction. Intermediate steps from different concurrent transactions do NOT interact (no cross-transaction rebase).