feat: impl CpcWrapper

[tisonkun]

This closes #99.

[Copilot]

Pull request overview

This PR implements CpcWrapper, a lightweight read-only view for extracting cardinality estimates from serialized CpcSketch data without performing full deserialization. This addresses issue #99 and aligns with similar implementations in the Go and Java DataSketches libraries.

Changes:

• Adds CpcWrapper struct that parses only the preamble from serialized CPC sketches to extract estimation parameters
• Refactors estimation logic from CpcSketch into shared functions in the estimator module for code reuse
• Extracts serialization constants and utilities into a dedicated serialization module

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
datasketches/src/cpc/wrapper.rs	Implements CpcWrapper with preamble-only parsing and estimation methods
datasketches/src/cpc/serialization.rs	Extracts shared serialization constants (flags, version) and preamble calculation function
datasketches/src/cpc/estimator.rs	Adds estimate/lower_bound/upper_bound wrapper functions and makes internal functions private
datasketches/src/cpc/sketch.rs	Refactors to use shared estimator and serialization utilities
datasketches/src/cpc/mod.rs	Adds serialization and wrapper modules, exports CpcWrapper
datasketches/tests/cpc_wrapper_test.rs	Tests wrapper functionality with HIP and ICON modes, error handling
CHANGELOG.md	Documents new CpcWrapper feature

---

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