Add unit tests for non-contiguous polygonToCells edge cases (#600)

[FurqanShafiq11]

Description

This PR addresses #600 by adding comprehensive unit tests for polygonToCells edge cases.

As discussed in #599, the library lacked tests for non-contiguous cell cases where the "outline-tracing" logic is required. These tests ensure that polygons with disjointed hexagonal regions (where the bridge between regions is too narrow to contain a hexagon center) are correctly processed.

Changes

• Added 4 test cases to src/apps/testapps/testPolygonToCells.c:
  • Barbell: Two lobes connected by a bridge thinner than a hexagon.
  • Splitting Hole: An interior hole that divides the polygon into two isolated hexagonal clusters.
  • Multi-Island Serpent: A winding polygon that results in 3+ disconnected cell clusters.
  • Transmeridian Barbell: A barbell shape that crosses the 180/-180 degree meridian.
• Updated CHANGELOG.md under the [Unreleased] section.

Verification

• Ran ./bin/testPolygonToCells locally.
• Assertion count increased by 12 (Current total: 120,824).
• Formatted code using clang-format (version 14).

Closes #600

[CLAassistant]

All committers have signed the CLA.

[coveralls]

coverage: 99.013%. remained the same
when pulling 65ee789 on FurqanShafiq11:tests/issue-600-polyfill-edge-cases
into 8085979 on uber:master.