By: David Nies <david.nies@posteo.de>
Share serialized graph check derivation Prior to this change, the GT and GraphML flake checks duplicated the same graph-tool Python environment, fixture staging, pytest invocation, and install phase. Only the serialized graph suffix and test directory differed between the two derivations. This change factors the common derivation into nix/checks/serialized-graph.nix and turns the GT and GraphML checks into thin wrappers that pass their format-specific suffix and test directory.
| Time to Start | Worker time | Duration | Time to finish | |
| Config | 2m29s | 7s | 7s | 2m37s |
| Eval | 2m37s | 1m28s | 1m28s | 4m05s |
| Build | 2m58s | 14m09s | 2m24s | 5m23s |
| Test | - | - | - | - |
| Deploy | - | - | - | - |
| Suite | 2m29s | 15m45s | 2m54s | 5m23s |