Fix Polygon2D convex hull winding direction

[JayLeo04]

Fixes#248.

Summary

• Correct the convex hull winding selection by passing !clockWise when sorting centroid-to-vertex vectors by their signed angle to the x-axis.
• Let three-point inputs use the same hull collection and ordering path, so the direction argument is honored for the smallest valid polygon.
• Correct the existing SciPy-generated test expectations to treat their 2-D order as counter-clockwise.
• Add regression coverage for clockwise, counter-clockwise, default, and triangle behavior using signed area.

Testing

• Updated convex hull tests: 7 passed. The same 7 tests fail against the unmodified implementation.
• Full NUnitLite suite on netcoreapp3.1: 1307 total, 1271 passed, 0 failed, 35 skipped, 1 inconclusive (pre-existing).
• Release build completed for both netcoreapp3.1 and net461.

[JayLeo04]

CI environment note: AppVeyor build 1.0.553 restored, compiled, and packed the solution successfully, then failed before running any tests because Microsoft.NETCore.App 3.1 is no longer installed on the current Visual Studio 2022 image. The available runtimes begin at 5.0, while Spatial.Tests targets netcoreapp3.1.

The repository's AppVeyor configuration downloads SDK 5.0.200 but relies on the image for the 3.1 runtime. For comparison, the previous build 1.0.552 found image-provided runtime 3.1.32 and completed both test runs successfully.

With runtime 3.1.32 installed locally, this PR's full NUnitLite suite completes with 1307 total, 1271 passed, 0 failed, 35 skipped, and 1 pre-existing inconclusive test. The Release build also succeeds for both netcoreapp3.1 and net461.