feat(library): Port PolyUtil to Kotlin and enhance tests

This commit introduces a significant modernization of the `PolyUtil` class by porting it from Java to idiomatic Kotlin. This change improves the code's conciseness, readability, and null safety.

The key changes in this commit are:
- **Porting `PolyUtil` to Kotlin**: The `PolyUtil` class has been completely rewritten in Kotlin, taking advantage of features like top-level functions, default arguments, and extension functions. The public API has been preserved with `@JvmStatic` annotations to ensure backward compatibility for Java consumers.
- **Updating tests to use Google Truth**: The corresponding `PolyUtilTest` has been updated to use Google Truth assertions. This makes the tests more readable and expressive.

Author: dkhawk