refactor: own SDS stored-state decoding and dataset-bound semantic identity

[zzylol]

Companion to the ASAPPlanner #462 split (ProjectASAP/ASAPPlanner#472–#475). Based on main; the Planner pin (4b0839c) is unchanged.

Before this PR

Backend used two things that are deployment concerns but lived in ASAPPlanner:

• SDS stored-state code from asap_physical_operators::stored_state: sketch frame decoding (modified-OTLP proto and msgpack), delta reconstruction, sketch readouts and native batch frames.
• Dataset-bound semantic identity from planner_types::post_asap::SummarySemanticFragment v2, which embedded LogicalDatasetIdentity inside the Planner fragment.

After this PR

Backend owns both. The new Planner layers drop them.

• sketch_db/query/{decoders,delta_apply,sketch_readout}.rs and sketch_db/data/native_batch.rs hold the SDS code, which used to be re-export shims.
• asap_types::semantic_fragment holds the v1 SemanticFragment (a structural dependency closure) and LogicalDatasetIdentity.
• The dataset is recorded next to the fragment:
  • PrecomputeMaterialization.dataset_identity;
  • SummarySemantics::Planner { dataset, fragment }.
• So tenant A's KLL(latency) and tenant B's KLL(latency) still get different SummaryDefinitionIds. The check against ingest.dataset_identity now compares the materialization's dataset.

Not in this PR

• Exact readouts (stored_state::readout::exact_readout[_optional]) are Planner semantics and are still called from the Planner at this pin.
• The physical plan byte format (CompiledPhysicalDag::encode/decode) moves when Backend bumps its Planner pin.

Validation

• cargo test --workspace: 1556 passed.
• cargo clippy --all-targets -D warnings and fmt --check: clean.
• New or updated tests:
  • dataset_identity_is_part_of_definition_id;
  • dataset_identity_survives_binding_and_rejects_wrong_input, which now also rejects a forged materialization dataset.
• The moved semantic_fragment and native_batch unit tests still run.

control_plane/build.rs needs Go on PATH, as before.

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