perf(graph): extend canonical edges without repeated NodeId clones

[jonathanong]

Summary

extend_edges_preserving_ordinals now uses map entry/get_mut APIs and moves accepted CanonicalEdges into adjacency so selector append does not clone NodeId five times per edge. Ordinals stay base-then-new; duplicates are still skipped.

Local Criterion (source of truth)

Machine: macOS aarch64, rustc 1.96.0, --sample-size 20, NO_MISTAKES_BENCH_SHARD=graph-production. Same machine before/after. CodSpeed is not used as a gate. Peak memory was not printed by this Criterion run.

bench	before (mean)	after (mean)	change
selector_append	55.646 ms	49.523 ms	−11.0%
node_id_finalization (control; path unchanged)	27.663 ms	26.039 ms	−5.0% (noise)

Shepherd Journal

• CodSpeed regressions reported different runtime environments; local Criterion selector_append −11%. No code change.
• First-look CodSpeed comment already minimized; different runtime environments; local Criterion selector_append −11%.
• Codex quota comments IC_kwDOSaSRXM8AAAABStKgwA/IC_kwDOSaSRXM8AAAABStKiwA and Sourcery budget review PRR_kwDOSaSRXM8AAAABMTHoGg are bot-limit notices, not code findings; minimize only.
• Codex quota comments IC_kwDOSaSRXM8AAAABStOecA/IC_kwDOSaSRXM8AAAABStQZ6A/IC_kwDOSaSRXM8AAAABStRqUQ are bot-limit notices; minimize only.
• Codex quota comment IC_kwDOSaSRXM8AAAABStTN5g is a bot-limit notice; minimize only.
• codecov/project/rust "No coverage information found on head" while native/Rust jobs are still inProgress is upload lag after restack, not a NodeId-clone defect.