feat(astra): add independent nesting engine and fix hole validation

Replace the Terra scaffold with an independent configuration-space contact placer and bounded stock-plan search. Include plugin tests, synthetic and DXF benchmark drivers, results, and deployment documentation.

Correct shared collision clipping and hole subtraction so curved-hole inserts validate consistently. Cover translated layouts, spacing violations, operand order, winding, and independent boolean-area comparisons.

Validation: 1,293 tests passed with 12 fixture skips; all 34 synthetic/generated and four DXF cases are valid and complete.

OpenNest.Engine.Astra/benchmarks/results/ring-validator-fixed.txt

@@ -0,0 +1,8 @@
+q=1 offset=0 valid=True:
+q=1 offset=0.0003 valid=True:
+q=1 offset=0.05 valid=True:
+q=1 offset=0.1 valid=True:
+q=2 offset=0 valid=True:
+q=2 offset=0.0003 valid=True:
+q=2 offset=0.05 valid=True:
+q=2 offset=0.1 valid=True: