Fix cylinder point containment

[killerdevildog]

Fixes #29

cylinderShape(1, 2).containsPoint(...) rejects (0, 0.75, 0), which is inside the cylinder, and accepts (0, -2, 0), which is outside. The radial check uses x*x + y + y, breaking the cylinder's symmetry.

Replace y + y with y * y so the check evaluates x*x + y*y. The two queries now return true and false, respectively.

Validation: built the standalone physics library in Debug mode with GCC 16.0.1 and ran all 13 geometry tests successfully. A local regression test failed before the fix and passed afterward with 30 assertions covering both signs of X/Y, two radii, and radial and cap boundaries. That test and the standalone reproducer are not included in this PR; this PR contains only the one-line implementation fix. The full project test suite was not run.

Local regression test

This is the test run from tests/geometryTests.cpp before applying the fix. It failed on the original implementation because containsPoint(Vec3(0.0, -2.0, 0.0)) returned true for a radius-1 cylinder, although the point is outside. After the fix, the same test passed all 30 assertions, and all 13 geometry tests passed. The failure demonstrated the existing bug; it was not a failure introduced by this PR.

The test is reproduced below for reference. It remains local and is not included in the committed changes.

TEST_CASE(testCylinderContainsPoint) {
	for(double radius : {1.0, 2.5}) {
		Shape cylinder = cylinderShape(radius, 4.0);
		ASSERT_TRUE(cylinder.containsPoint(Vec3(0.0, 0.0, 0.0)));
		for(double sign : {-1.0, 1.0}) {
			ASSERT_TRUE(cylinder.containsPoint(Vec3(sign * 0.75 * radius, 0.0, 0.0)));
			ASSERT_TRUE(cylinder.containsPoint(Vec3(0.0, sign * 0.75 * radius, 0.0)));
			ASSERT_FALSE(cylinder.containsPoint(Vec3(sign * 2.0 * radius, 0.0, 0.0)));
			ASSERT_FALSE(cylinder.containsPoint(Vec3(0.0, sign * 2.0 * radius, 0.0)));
			ASSERT_TRUE(cylinder.containsPoint(Vec3(0.0, sign * radius, 0.0)));
			ASSERT_TRUE(cylinder.containsPoint(Vec3(0.0, 0.0, sign * 2.0)));
			ASSERT_FALSE(cylinder.containsPoint(Vec3(0.0, 0.0, sign * 2.5)));
		}
	}
}

[VonTum]

Oh, you are correct. Well spotted.