feat: 新增月掩与日月食地理绘图并提升观测计算精度

- 新增月掩恒星和行星：支持搜索、掩甚点、全球掩带及固定地点轨迹计算
- 支持恒星星表坐标转换、有限盘面行星接触事件和月掩 SVG 输出
- 新增日月食及月掩全球投影图、时间标记和 GeoJSON 地理数据接口
- 扩展日食中心线、南北界及偏食足迹采样，支持极区投影
- 修正站心时角、月出月落、月球视半径、折射和恒星自行计算
- 优化内外行星事件搜索、边界选择、极端输入处理和计算稳定性

internal/geodata/topology_test.go

@@ -0,0 +1,37 @@
+package geodata
+
+import (
+	"math"
+	"testing"
+)
+
+func TestPolylineSegmentsTreatsExactAntimeridianAsOneMeridian(t *testing.T) {
+	segments := PolylineSegments([]GeoPoint{
+		{Longitude: -180, Latitude: 10},
+		{Longitude: 180, Latitude: 20},
+	}, ProjectionEquirectangular)
+	if len(segments) != 1 || len(segments[0]) != 2 {
+		t.Fatalf("exact-antimeridian line segments = %#v", segments)
+	}
+	if segments[0][0].Longitude != segments[0][1].Longitude {
+		t.Fatalf("exact-antimeridian line spans %.1f degrees",
+			math.Abs(segments[0][1].Longitude-segments[0][0].Longitude))
+	}
+}
+
+func TestPolygonFragmentsDropsExactAntimeridianZeroAreaDuplicate(t *testing.T) {
+	fragments := PolygonFragments([]GeoPoint{
+		{Longitude: -180, Latitude: 15},
+		{Longitude: 180, Latitude: 14},
+		{Longitude: 150, Latitude: 13},
+		{Longitude: 150, Latitude: -12},
+		{Longitude: 180, Latitude: -11},
+		{Longitude: -180, Latitude: -10},
+	}, ProjectionEquirectangular)
+	if len(fragments) != 1 {
+		t.Fatalf("exact-antimeridian polygon produced %d fragments, want 1", len(fragments))
+	}
+	if math.Abs(signedPolygonArea(fragments[0])) < 1e-12 {
+		t.Fatal("exact-antimeridian polygon fragment has zero area")
+	}
+}