Create tests/unit/subscription_handle_test.py

[exploreriii]

We have a src/hiero_sdk_python/utils/subscription_handle.py
but have no unit tests for each

We should test its functionality

[Giannis-dot]

i want to work on this issue. Can you assign it to me?

[exploreriii]

Hi @Giannis-dot please create a PR in this repository

[exploreriii]

Closed as completed via #1028