[graph] Reduce metadata overhead of slice realizer

[graph] Reduce metadata overhead of slice realizer

Slice realizer was storing the path for each node from the start nodes
to themselves. This can be big, and also comes with a overhead of
storing and copying these paths for each node.

This patch updates the implementation of the dfs to a recursive approach
which maintains the stack of the nodes in the memory which represents
the path till now.

Signed-off-by: Parichay Kapoor <pk.kapoor@samsung.com>