Expose deterministic batch-cost estimates before accepting large payout requests

[Jagadeeshftw]

Problem

Large payout batches can be accepted without a predictable resource-cost estimate, creating avoidable transaction failures.

Scope

Add a read-only estimator based on recipient count, storage work, and transfer behavior, with conservative bounds.

Acceptance criteria

• The estimate is deterministic for identical state and input.
• The estimator never claims a batch is safe when it exceeds configured limits.
• Boundary tests cover empty, normal, and maximum batches.

Validation

Compare estimates with measured resource usage in benchmark fixtures.