Applies a list of %Milvex.Migration.Plan{} against a live Milvus cluster.

The runner is the only module in the migration pipeline that issues mutating RPCs. It walks the plans sequentially and applies each operation per the rules in apply/2:

• If any plan in the batch contains an :impossible operation, the runner returns immediately. No RPC is attempted; every non-impossible operation across all plans is reported as :blocked_by_impossible and every :impossible op as :blocked_impossible.
• For each plan, when manage_load: true AND any operation in that plan requires release AND the live collection is loaded, the runner releases the collection before applying the operations and re-loads it after.
• Operations are applied in plan order. :additive ops always run. :destructive ops run only when allow_drop: true; otherwise they are :skipped_no_flag. :descriptive ops always come back as :skipped_idempotent and never go through the dispatch path.
• Per-operation RPC failures DO NOT abort the plan. The failure is recorded and the runner moves on to the next op. Release / reload failures DO abort the plan (no further ops attempted on release failure; ops up to the failure point are kept on reload failure).
• Plans are isolated. A failure in one plan never leaks load state to the next plan.

The runner emits :telemetry spans:

• Run-level: [:milvex, :migrate, :run, :start | :stop | :exception] with start metadata %{mode, allow_drop, manage_load} and stop metadata %{summary: counts}.

• Op-level: [:milvex, :migrate, :op, :start | :stop | :exception] with start metadata %{kind, category, collection_name, module, requires_release, milvus_version} and stop metadata %{result: status}. Only operations that actually reach the dispatch path emit telemetry; skipped/blocked ops do not.