Land T2.7: a non-SQL test provider and a second data layer at the composition root

Both reviews approve the candidate 126c867.

Candidate run 39261909822 green at
126c867; this commit changes no file,
so the phase branch moves at once and CI skips its own runs (E43 (b),
E131).

Reviewed-by: independent reviewer (fresh agent) and Codex, T2.7
Protected-paths: contract/fixtures/provider-kit/expected.json; contract/tests/t27-pending.json; rust/crates/sdm-testkit/Cargo.toml; rust/crates/sdm-testkit/src/bin/sdm-contract-run.rs; rust/crates/sdm-testkit/src/host.rs; rust/crates/sdm-testkit/src/kit.rs; rust/crates/sdm-testkit/src/layer.rs; rust/crates/sdm-testkit/src/lib.rs; rust/crates/sdm-testkit/src/memory.rs; rust/crates/sdm-testkit/tests/memory_provider.rs; rust/crates/sdm-testkit/tests/t27_non_sql_provider.rs
Base-SHA: cfdbbaa
Checkpoint-SHA: cfdbbaa
Signed-off-by: Adi Wadaskar <awadaskar@nvidia.com>

Author: adi-kumo