Add petgraph algorithms kosaraju_scc and tarjan_scc #8

[code-ape]

Work in progress, added rough version of functions and tests. Needs refinement and better testing of ergonomics for resulting JsValue of SccGroups.

Changes

NOTICE: Will update this with proper details of changes once pre-requisite PRs have been merged.

1. GitHub Actions CI now properly uses cache. Time down 75% from ~180 seconds to ~45 seconds. Cache size per rust version is ~200MB.

Action Items

• Split out cache fix into pre-requisite PR (Fixing Actions CI caching not working #11).
• Split out test structure change into pre-requisite PR (Moved unit tests to src/ #12).
• Split out src/js_helpers/vec_tree.rs into pre-requisite PR. (Add VecTree for generic N-dimensional Vec structures #10 #13)
• Add JS iterators for SccGroups and SccGroup for easy traversal.

[code-ape]

Filed "petgraph/petgraph#409: Inconsistencies in scc algorithms" as found while working on this.