Add isLongZero check for SignScheduleTranslator.getScheduleIDFromCall

### Background

While implementing https://github.com/hiero-ledger/hiero-consensus-node/issues/20054 we [decided](https://github.com/hiero-ledger/hiero-consensus-node/pull/20437#discussion_r2248297812) to add `isLongZero` check for `DeleteScheduleTranslator`. Looking into [SignScheduleTranslator.getScheduleIDFromCall](https://github.com/hiero-ledger/hiero-consensus-node/blob/503927c9224cec8e87bac8368536717518dda501/hedera-node/hedera-smart-contract-service-impl/src/main/java/com/hedera/node/app/service/contract/impl/exec/systemcontracts/hss/signschedule/SignScheduleTranslator.java#L171) `isLongZero` check also should be added to keep logic similar.

### Acceptance Criteria

1. `isLongZero` check added to `SignScheduleTranslator.getScheduleIDFromCall`
2. tests changed to support new validation

Open SignScheduleTranslator.java and inspect getScheduleIDFromCall, comparing its validation with the referenced DeleteScheduleTranslator logic. Locate the tests for this translator, add coverage for the new isLongZero validation, and confirm the updated tests pass.

Written by the indexing model from the issue text.