feat: implemented transient arguement for the coindex.flow_def decorator

[shresthashim]

Issue : #998

I have successfully implemented the transient argument for the @cocoindex.flow_def decorator as requested.

Updated flow_def decorator
Updated open_flow function
Updated _create_lazy_function
Created TransientFlowWrapper class

Now users can create transient flows like this :
@cocoindex.flow_def(name="MyFlow", transient=True)
def my_flow(flow_builder: cocoindex.FlowBuilder, data_scope: cocoindex.DataScope):
# Flow definition that works with inputs and produces outputs
# but doesn't maintain persistent state
pass

[badmonster0]

Hi @shresthashim thank you so much for your contribution! We cannot accept this one since it is different than the expected behavior . Detailed explanation here #998 (comment) . thanks