ODRE import postprocessor fixes

[flo-dup]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem? No

What kind of change does this PR introduce? Cleaning post processor code

What is the current behavior?

• 40s on my laptop to import all the lines & substations positions
• 3 graph traversals for each line
• coordinates duplicated if same line reference twice with code_ligne_x and code_ligne_y
• code duplication
• substations read twice

What is the new behavior (if this is a feature change)?

• 5s on my laptop to import all the lines & substations positions
• graph not created if only one entry
• one single graph traversal for each problematic line
• coordinates not duplicated if same line reference twice with code_ligne_x and code_ligne_y
• code factorization
• substations read once

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [x] No