refactor(asap-planner-rs): extract shared helpers for SQL/PromQL extensibility

[milindsrivastava1997]

This PR just refactors some code in asap-planner-rs in preparation for adding SQL support.
SQL support is being added in #227 but that PR was being unwieldly so splitting into multiple PRs.

Created

• build_sketch_parameters — core sketch param builder, query-language-agnostic
• build_sketch_parameters_from_promql — PromQL wrapper around build_sketch_parameters
• build_aggregation_entry — builds a single aggregation YAML entry
• build_queries_yaml — builds the full queries YAML block
• build_agg_configs_for_statistics — aggregation config loop, shared by both paths
• get_sql_cleanup_param — SQL-specific cleanup param helper
• get_label_routing — replaces compute_labels, extracts rollup/subpopulation label routing logic

Updated

• parse_cleanup_policy, key_by_labels_to_yaml, params_to_yaml — made pub

Deleted

• get_precompute_operator_parameters — replaced by build_sketch_parameters + build_sketch_parameters_from_promql
• compute_labels — replaced by get_label_routing

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com