feat(control_plane): plumb per-metric sample_p from workload to agent emit

[zzylol]

Summary

Add an optional per-metric sketch sampling probability p so an operator can turn on the warm-sketch sampling per metric from the control plane.

• WorkloadEntry gains a sample_p field (workload YAML, default 1.0 = sampling disabled).
• The planner threads it into EdgeStageConfig.metric_to_sample_p via a new collect_metric_to_sample_p collector — wired in both the bootstrap (main::emit_bootstrap_typed) and replan (replan.rs) paths, mirroring the existing metric_to_grouping_labels / cumulative_counter_metrics stitch.
• The L5 edge emitter writes a sample_p knob onto the CMS / HLL sketch-processor block in build_edge_processor_block (and the fused asap_edge per-metric entries), via a shared insert_sample_p helper guarded so it is only emitted when p < 1.

Full path (file:func at each hop)

1. control_plane/src/workload.rs — WorkloadEntry::sample_p (operator field, default 1.0).
2. control_plane/src/emit/mod.rs — collect_metric_to_sample_p() (validates (0,1], skips 1.0/out-of-range).
3. control_plane/src/main.rs::emit_bootstrap_typed + replan.rs — stitch into EdgeStageConfig.metric_to_sample_p.
4. control_plane/src/physical/colored_dag/emitter.rs — EdgeStageConfig::metric_to_sample_p field.
5. control_plane/src/emit/stage_config.rs::build_edge_processor_block → insert_sample_p — emits sample_p: on the CMS/HLL agent YAML block.
6. → agent countminsketchprocessor/hllprocessor Config.SampleP → sketchlib-go WithSampleP (companion agent PR).

Default 1.0 everywhere keeps the map empty and emits no sample_p key ⇒ byte-identical agent config when unset.

Test plan

• cargo build + cargo test green (775 lib + 28 integration).
• Tests: WorkloadEntry.sample_p default/parse; a configured p<1 reaches the emitted agent YAML for CMS + HLL; 1.0/unset emits nothing.
• No shared-type-by-literal break introduced. cargo check --bin data_plane is currently red in this checkout due to a pre-existing asap-precompute-rs vs asap_sketchlib proto skew (missing sample_p/registers_sparse in regenerated proto, plus renamed sketch types) — asap-precompute-rs fails standalone, independent of this PR. This change is additive control-plane-internal types; cargo build -p control_plane (what data_plane's control_plane dep needs) is green.

Merge order

Merge the agent PR first: ProjectASAP/ASAPCollector#441 (CMS/HLL processor sample_p + precompute WithSampleP). This PR emits that agent config.

Out of scope / follow-up

Dynamic, optimizer-driven p (tuned online from runtime samples against an accuracy/bandwidth budget) — this PR ships only the static per-metric knob.

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