refactor(hll): reuse the inverse powers lookup table

[tisonkun]

No description provided.

[Copilot]

Pull request overview

This PR refactors the HLL HIP estimator to reuse the existing shared INVERSE_POWERS_OF_2 lookup table (previously used by CPC), removing the local inv_pow2 helper and enabling the shared table module when the hll feature is selected.

Changes:

• Switched HIP KxQ updates to use INVERSE_POWERS_OF_2[...] table lookups instead of inv_pow2(...).
• Removed the now-redundant local inv_pow2 function from hll/estimator.rs.
• Expanded common::inv_pow2_table module gating to compile under either cpc or hll features.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
datasketches/src/hll/estimator.rs	Uses the shared inverse-powers table for HIP KxQ accumulation and removes the local inverse-power helper.
datasketches/src/common/mod.rs	Makes inv_pow2_table available when building with the hll feature.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.