Process flows more efficiency in network observer (#1940)

* Process flows more efficiency in network observer

The network observer handles an in memory buffer of application and
transport level flow records and associated state that can be very
large. This changes how those collections are traversed for processing.
Previously the collections of flow state were copied on each reconcile
loop, resulting in high CPU and memory utilization. Now each reconcile
job limits itself to copying the relevant portions by using an iterator
and filters.

Signed-off-by: Christian Kruse <[email protected]>

* Reorganize and add flow reconcile tests

Signed-off-by: Christian Kruse <[email protected]>

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Signed-off-by: Christian Kruse <[email protected]>