fix(interop): preserve typed-array backing slices

[nnunley]

Summary

• preserve compatible TypedArray backing slices at the Go reflection boundary
• keep generic vector/list and incompatible-element conversion behavior unchanged
• cover backing identity and host mutation for byte, int, float, object, and named slice types
• reproduce io.Reader.Read at the language level and verify caller-visible bytes

Verification

• focused VM/API/language regression tests
• focused race tests
• go vet ./pkg/vm ./pkg/api ./test
• full go test ./pkg/vm ./pkg/api
• all Go-level ./test tests outside the fixture runner
• make generate
• make check-generated
• independent review: PASS

The full local fixture runner was also attempted: 810 tests passed and 10 fixture cases failed only because this sandbox denies writes to literal /tmp paths. The exact #813 regression passes.

Fixes #813

[mparrett]

No actionable findings. The compatible-slice fast path preserves TypedArray backing identity while retaining the existing conversion path for fixed arrays, incompatible element types, and persistent collections. Focused VM/API/language tests, race tests, vet, and generated-artifact validation pass; CI is green.