refcator to isolate the code in `startRuntimeInterfaceClient` and
`startLocalServer` functions
Also change the name of the global variable `_isRunning` to
`_isLambdaRuntimeRunning`
Co-authored-by: Sebastien Stormacq <stormacq@amazon.lu>
This PR removes `Sendable` requirement on `StreamingClosureHandler `.
While analyzing code for the upcoming support of Lambda Managed Runtime,
I found out that `StreamingClosureHandler` has `Sendable` requirement,
which is not necessary.
Removing requirement doesn't require a major speed bump as the change is
compatible with existing code.