feat: propagate blind and buried via board option

[seveibar]

Summary

• serialize <board allowBlindAndBuriedVias> to Circuit JSON as allow_blind_and_buried_vias
• always materialize false for an actual board unless it explicitly opts in
• translate the Circuit JSON field to Simple Route JSON as allowBlindAndBuriedVias
• preserve legacy standalone/group behavior by omitting the Simple Route JSON field when no pcb_board exists

Cross-repository stack

• public board prop: tscircuit/props#808
• Circuit JSON transport: tscircuit/circuit-json#719
• autorouter enforcement: tscircuit/tscircuit-autorouter#2200

This PR remains a draft until the props and Circuit JSON packages above are published. It was built and tested locally against their exact clean feature commits (4365a56 and 97189da).

Contract

For board-backed routing, false requests full-stack newly generated vias and true permits blind and buried generated vias. Existing authored partial-depth vias are not rewritten. A boardless conversion omits the field so standalone callers retain the autorouter's legacy compatibility behavior.

Validation

• all autorouting utility tests, the two board propagation tests, and all three affected inline snapshots — 42 pass, 0 fail, 4 snapshots, 126 assertions
• one test per newly added Core test file
• bunx tsc --noEmit against the exact local props/Circuit JSON builds
• bun run build against the exact local props/Circuit JSON builds
• bun run format
• git diff --check

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Project	Deployment	Actions	Updated (UTC)
tscircuit-core-benchmarks	Ready	Preview	Aug 22, 2026 6:26pm

[github-actions]

This PR has been automatically marked as stale because it has had no recent activity. It will be closed if no further activity occurs.