[Feature] [Python] Drop ChipStack network lock

[agners]

Feature description

Currently several places which call PostTaskOnChipThread take a networkLock in the ChipStack class. It is not clear what this lock exactly protects. From the the function ultimately calls ScheduleWork from src/include/platform/PlatformManager.h, which should be safe to be called from any Thread:

 * ScheduleWork can be called safely on any thread without locking the
* stack.  When called from a thread that is not doing the stack work item
* processing, the callback function may be called (on the work item
* processing thread) before ScheduleWork returns.

Platform

python

Platform Version(s)

No response

Anything else?

No response