Harden graph algorithms and batch operations

[davidkpiano]

Summary

• enforce finite weights, capacities, and accumulated costs across shortest paths, spanning trees, and flow
• add getUnweightedDistances, isWeaklyConnected, and isStronglyConnected
• make low-link connectivity iterative and stack-safe with multigraph/self-loop coverage
• snapshot transform inputs and make iterable bulk deletion a single mutation pass
• update public docs and add a minor changeset

Verification

• pnpm verify
• 83 test files, 1,880 tests passed

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.