feat: implement count-min sketch

[PsiACE]

Related to #35

• Implement Count-Min sketch.
• Add unit tests for core behavior, merge, serialization, and cases adapted from rust-count-min-sketch.

[Copilot]

Pull request overview

This PR implements a Count-Min sketch data structure for approximate frequency counting in streaming data. The implementation provides configurable accuracy through relative error and confidence parameters, supports negative weights, and includes serialization/deserialization compatibility with the DataSketches format.

Key changes:

• Core Count-Min sketch with update, estimate, merge, and bound calculation operations
• Helper functions for parameter suggestions based on desired error and confidence levels
• Serialization support compatible with DataSketches Count-Min format
• Comprehensive test suite covering basic operations, edge cases, and serialization

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/lib.rs	Adds countmin module to the library's public API
src/countmin/mod.rs	Module definition with documentation and public exports
src/countmin/sketch.rs	Core Count-Min sketch implementation with update, estimation, merge, and serialization methods
src/countmin/serialization.rs	Serialization constants and helper functions for DataSketches format compatibility
tests/countmin_test.rs	Comprehensive test suite covering initialization, updates, bounds, merge, serialization, and edge cases

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[notfilippo]

Cool! Thanks. I'll take a look soon...