feat(ingest): consume asap-precompute-rs for envelope/delta/merge logic

[zzylol]

Summary

• Phase 3 step 3 of the ASAP edge-framework migration. Backend ingest path now delegates the shared envelope-parsing, sketch-reconstruction, and merge logic to asap-precompute-rs (the host-neutral Rust edge runtime). The same code now runs in agents and the backend.
• New module asap-query-engine/src/precompute_operators/edge_runtime_adapter.rs re-exports asap-precompute-rs's runtime view types (SketchEnvelope, Encoding, SketchType, the Sketch trait family) and exposes reconstruct_via_runtime / unwrap_envelope_state / encode_ddsketch_envelope / merge_ddsketches_via_runtime helpers used by the decode_modified_otlp_sketch_bytes hot path.
• DDSketch and KLL byte parity is live (upstream asap_sketchlib PRs feat(sketch-db): create_checked retention validation (Method B) #40, feat(sketch-db): Phase 5 eviction — SchemaEvictionService background task #41). HLL / CountSketch / CountMinSketch byte parity is tracked under ProjectASAP/ASAPCollector#243; their tests are gated #[ignore = "blocked on ASAPCollector#243 HLL/CS/CMS byte parity"].
• Query-side engine is unchanged: PromQL aggregation, storage, and query planning all stay in this repo. Backend's per-accumulator AggregateCore / query_statistic / MergeableAccumulator traits stay; sparse-delta apply (apply_modified_otlp_delta_bytes) stays.

Notable details

• DDSketch / KLL ingest paths in decode_modified_otlp_sketch_bytes try the runtime adapter first (envelope-wrapped wire format, the canonical edge-framework shape). On envelope-decode failure (bare *State proto, as some unit-test / pre-envelope payloads still emit per the PR fix(ingest): decode envelope-wrapped CountMinState from DC processor #14 contract on from_sketchlib_proto_bytes), the dispatcher falls back to the backend's existing native decoder so existing e2e tests keep working unchanged.
• HLL / CountSketch / CountMinSketch ingest still uses backend's per-accumulator decoders until refactor(emit): re-target agent OTLP export from gateway:4317 → backend:4317 #243 lands.
• Workspace Cargo.toml adds a [patch."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/ProjectASAP/asap_sketchlib"] block pointing at the local ../asap_sketchlib checkout. This is required so the asap_sketchlib::sketches::* types unify across the two consumers (backend's git-sourced dep and asap-precompute-rs's path-sourced dep) at the FFI boundary (wrapper.inner() → backend accumulator).
• asap-precompute-rs is consumed via a sibling path dep (../../ASAPCollector/asap-precompute-rs) — see the comment in asap-query-engine/Cargo.toml for why git-source resolution doesn't work today (parent-repo submodule pins).

Test plan

• cargo build --workspace (succeeds)
• cargo test --workspace --no-run (all test binaries compile)
• cargo test --test edge_runtime_consumes_precompute_rs (6 passed, 3 ignored)
• cargo test --test e2e_modified_otlp_sketch_path (6/6 passed; DDSketch + KLL routes through new adapter, others use backend's native decoder)
• cargo test --lib precompute_operators::edge_runtime_adapter (3 unit tests pass: round-trip, merge, envelope unwrap)
• HLL / CountSketch / CountMinSketch round-trip tests are present and #[ignore]'d pending ASAPCollector#243.

Note: the workspace lib has 35 pre-existing test failures in tests::datafusion::* / tests::elastic_* / tests::prometheus_forwarding_tests / tests::schema_timeline_dispatch_tests paths. These exist on origin/main and are unrelated to this PR's ingest/adapter work.