Add unit tests for gov.nasa.jpf.util.WeakPool

[HritikRaj2]

Description

This PR adds a new test class gov.nasa.jpf.test.util.WeakPoolTest to improve coverage for the gov.nasa.jpf.util package.

WeakPool is a critical utility for canonicalizing objects using WeakReference, allowing unused objects to be reclaimed by the Garbage Collector.

Changes

• Created src/tests/gov/nasa/jpf/test/util/WeakPoolTest.java

Tests Added

1. testBasicPooling: Verifies standard pool operations (add, check existence, deduplication).
2. testWeakReferenceBehavior: (Key Test) Forces a System.gc() to verify that the pool correctly handles objects being collected when strong references are dropped.
3. testGrowth: Ensures the pool resizes correctly when capacity is exceeded.

Verification

• Ran ./gradlew test
• Result: Build Successful (All tests passed).

Fixes #593

[HritikRaj2]

@cyrille-artho
If you get some time, please look at this pr and tell me if any changes are required or not .
and these prs too #592 and #596