asap-query-engine: integrate asap-planner-rs library for in-process config generation

[milindsrivastava1997]

Problem

asap-planner-rs already exposes a Rust library crate (asap_planner), but asap-query-engine has no dependency on it and cannot invoke config generation in-process. This is a prerequisite for the embedded auto-discovery query tracker.

Goal

Wire asap-query-engine to call the asap_planner library directly when it needs to generate sketch configs from observed queries.

Details

• Add asap_planner as a workspace dependency in asap-query-engine/Cargo.toml
• Identify the correct public API entry points in asap_planner::lib for generating inference_config and streaming_config structs from a list of PromQL expressions
• Expose an internal PlannerClient trait/struct in asap-query-engine that wraps the library call, so it can be swapped for a mock in tests
• The embedded query tracker (separate issue) will call this once it identifies queries worth accelerating

Acceptance Criteria

• asap-query-engine compiles with asap_planner as a dependency
• A unit test demonstrates calling planner config generation in-process from asap-query-engine with a sample PromQL expression
• No user-facing change: the planner binary remains usable standalone

Notes

asap-planner-rs is already structured as [lib] + [[bin]], so no refactoring of the planner is needed — this is purely an integration task on the asap-query-engine side.