Client should not shutdown provided executor

[OlegMazurov]

Description

#1844 introduced a new API that allowed creating Clients with an external Executor. Multiple Clients can now share the same executor. However, when a Client is closed it shuts down its executor no matter whether it was provided or created by the client itself. That affects multiple clients sharing the same executor, reusing the executor for a client that had to be restarted, and lots of other scenarios where users assume control over their executor.

Steps to reproduce

• Create two Clients with the same external executor
• Close one Client
• Continue using the second Client

Additional context

No response

Hedera network

other

Version

2.39.0

Operating system

Linux