fix true edge index issues

[klieret]

• Renames: edge_index -> true_edge_index
• Make sure that true_edge_index is not overwritten

[codecov[bot]]

Codecov Report

Patch coverage: 42.85% and project coverage change: -0.06% :warning:

Comparison is base (83561e8) 71.98% compared to head (dffb31b) 71.92%. Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #393 +/- ## ========================================== - Coverage 71.98% 71.92% -0.06% ========================================== Files 49 49 Lines 3327 3338 +11 ========================================== + Hits 2395 2401 +6 - Misses 932 937 +5 ``` | [Files Changed](https://app.codecov.io/gh/gnn-tracking/gnn_tracking/pull/393?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gnn-tracking) | Coverage Δ | | |---|---|---| | [src/gnn\_tracking/models/graph\_construction.py](https://app.codecov.io/gh/gnn-tracking/gnn_tracking/pull/393?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gnn-tracking#diff-c3JjL2dubl90cmFja2luZy9tb2RlbHMvZ3JhcGhfY29uc3RydWN0aW9uLnB5) | `60.64% <0.00%> (-1.00%)` | :arrow_down: | | [src/gnn\_tracking/metrics/losses.py](https://app.codecov.io/gh/gnn-tracking/gnn_tracking/pull/393?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gnn-tracking#diff-c3JjL2dubl90cmFja2luZy9tZXRyaWNzL2xvc3Nlcy5weQ==) | `76.71% <50.00%> (ø)` | | | [src/gnn\_tracking/training/ml.py](https://app.codecov.io/gh/gnn-tracking/gnn_tracking/pull/393?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gnn-tracking#diff-c3JjL2dubl90cmFja2luZy90cmFpbmluZy9tbC5weQ==) | `100.00% <100.00%> (ø)` | |

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