Refactor network_x_processor

### What to refactor?

- Currently, there are plenty of loops across `G.nodes` list which could be optimized in some way.
- `app/network_x_tools/network_x_processor.py` could be also used to do general operations with DiGraph (G) such as:
- search.
- get effects
- get solutions

### Refactor reason

Code duplication and PEP8

### Tests

- [ ] unit tests

Start by reading app/network_x_tools/network_x_processor.py and tracing the existing loops across G.nodes. Identify the duplicated graph operations described in the issue, then add unit tests for the resulting behavior before confirming the refactor preserves search, effects, and solutions handling.

Written by the indexing model from the issue text.