mesh: exact predicates (Shewchuk adaptive, symbolic perturbation, indirect LPI/TPI) (#8)

* mesh: exact predicates (Shewchuk adaptive orient/incircle/insphere), symbolic perturbation, indirect LPI/TPI predicates

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* mesh: predicate benchmark (filter hit rate, CAD-degenerate inputs); record the predicate decision

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* mesh: simplify predicates (destructuring over fallbacks, shared-minor exact insphere, cheaper expansion product)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

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Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/mesh/Cargo.toml

@@ -11,3 +11,11 @@ workspace = true
 [dependencies]
 modelcraft-model = { workspace = true }
 thiserror = { workspace = true }
+
+[dev-dependencies]
+# Test oracles only (never linked into ModelCraft): exact rationals, and georust's port of
+# Shewchuk's public-domain predicates.c as a differential reference.
+num-bigint = "0.4"
+num-rational = { version = "0.4", default-features = false, features = ["num-bigint", "std"] }
+num-traits = "0.2"
+robust = "1.2"