ENH: add core score action

[VinzentRisch]

Summary

Adds a core score action that computes per-feature prevalence-abundance scores from a relative-frequency feature table and emits them as FeatureData[Importance].

Changes

• Adds core_score to compute scaled prevalence, scaled log mean abundance, and their product per feature.
• Registers the core_score method for FeatureTable[RelativeFrequency] inputs and FeatureData[Importance] outputs.
• Exports core_score from q2_feature_table.
• Adds targeted unit tests for default scoring, custom threshold/epsilon behavior, mean abundance over present samples, and finite scaling for constant values.

Links

• Closes ENH: add action to calculate core score for features #357
• Depends on MAINT: move Importance formats and type to q2-types q2-types#390

This PR was created in part with Codex 5.5

[lizgehret]

Hey @VinzentRisch once that q2-types PR is merged, we can rerun CI on this - just let us know when that's ready and you need a review on this one!

[VinzentRisch]

This was moved to q2-core