stack-encrypt tests: consolidate duplicate expectations after coverage parity #1481

Conformance should reduce duplicated semantic case tables while continuing to execute each language's implementation.

Acceptance:

• Use conformance/stack-encrypt/coverage.md to map candidate old assertions to stable shared case IDs and execution paths.
• Move remaining duplicate declaration/value/query expectations into their owning shared corpus or existing fixture.
• Compare coverage and failure behavior before deleting any old rows; preserve unrelated assertions in mixed-purpose tests.
• Retain Rust compile-fail, ownership/zeroization, batching and fuzz/property tests; retain Go generation, host conversion, error wrapping, cancellation and guest lifecycle tests.
• Keep independent PostgreSQL oracles and live-provider coverage.
• Run both consumers in CI and document each consolidation with its replacement evidence.

Proceed incrementally alongside #1477 and #1476. Enrollment in #1474 alone is not grounds to delete tests.

Plan: conformance roadmap and API redesign #1365.