By: Lucien Huber <im@lcnbr.ch>
deduplicate Rust workspace source and manifest definitions Share source-category selection and per-package source metadata, consolidate three synthetic Cargo manifest templates, and use existing genAttrs operations. Remove 88 lines without changing build inputs, commands, features or cache keys. All 413 public derivation/output pairs across three supported platforms remain identical. Temporary FeynKit integration preserves all 178 pairs in each of three scenarios: clean, GammaLoop source edit and CFF source edit. Selected CI checks pass from cache. No Cargo manifests or tests are changed. User request: yes, also we can think about simplifying the actual features/ cargo.toml setup too right?