refactor(batcher): change`is_batch_ready` to accomodate the `Result` from `try_build_batch` function

[entropidelic]

Once #1008 is merged, the is_batch_ready function should be refactored to accomodate to the new return value of try_build_batch function. If an error that is not of type BatcherError::BatchCostTooHigh, the error is being ignored.