Collapse per-variant test clusters in api-model, rpc, and uuid

[chet]

Three already-migrated crates still carry pockets of one-test-per-variant and self-referential tests the first pass didn't reach. Folding them into carbide-test-support tables puts the covered input space in one readable place and removes boilerplate; a few tests that only exercise a derive or restate a constant can go entirely. Test-only; no behavior change.

Scope

api-model

• Collapse the five is_power_shelf_* tests (site_explorer/mod.rs) into one value_scenarios! table.
• Merge build_version_partial_cmp_matches_cmp into the existing build_version_ordering table (machine/upgrade_policy.rs).
• Drop test_display_matches_debug (controller_outcome.rs) -- Display is defined as Debug::fmt, so it cannot fail -- and the AssignStaticResult PartialEq-derive table (allocation_type.rs).
• Drop the two IpAddr stdlib-format tests (machine/network.rs).

rpc

• Collapse the seven per-type MachineCapability* Check tests into one check_cases table (model/machine/capabilities.rs).
• Drop the two identity_config_try_from_proto_* tests that duplicate exact rows of the existing error-case table (model/tenant.rs).

uuid

• Merge the parallel RackId / RackProfileId parse + serde tests (rack/mod.rs).
• Drop the tautological *_conversions tests (transparent newtype: as_str == to_string == as_ref) and the test_db_column_name arm of typed_uuid_tests! (restates a constant against its own definition).

Acceptance

• Coverage preserved or improved; no production code changes.
• cargo test green for the three crates; cargo clippy --all-features clean.

Size: S-M

Part of #2692.