feat: 完善时标与天象几何计算并扩展输出接口

- 新增时标、ΔT 模型、质心时间与 UT1 支持
- 改进日月食、月掩、行星事件及路径边界计算
- 完善恒星三维自行与动态距离传播
- 扩展 SVG、GeoJSON、KML 输出与底层距离换算工具
- 整理中英文手册、示例资源及回归测试

tools/distance_test.go

@@ -0,0 +1,49 @@
+package tools
+
+import (
+	"math"
+	"testing"
+)
+
+// 参考值由同一组 IAU 定义值独立推出，不使用 9 位凑整常数。
+const (
+	testPcPerLy = LightYearKilometers / AstronomicalUnitKilometers / parsecAU
+	testAuPerLy = LightYearKilometers / AstronomicalUnitKilometers
+)
+
+func assertDistanceClose(t *testing.T, name string, got, want, tolerance float64) {
+	t.Helper()
+	if math.Abs(got-want) > tolerance {
+		t.Fatalf("%s mismatch: got %.15f want %.15f", name, got, want)
+	}
+}
+
+func TestDistanceToParsecsUnits(t *testing.T) {
+	assertDistanceClose(t, "1 pc", DistanceToParsecs(1, DistanceParsec), 1, 1e-15)
+	assertDistanceClose(t, "1 ly in pc", DistanceToParsecs(1, DistanceLightYear), testPcPerLy, 1e-15)
+	assertDistanceClose(t, "1 ly in pc 参考 0.3066", testPcPerLy, 0.306601394, 1e-9)
+	assertDistanceClose(t, "1 pc in ly 参考 3.261563777", 1/testPcPerLy, 3.261563777, 1e-9)
+	assertDistanceClose(t, "1 ly in au 参考 63241.077084", DistanceToParsecs(1, DistanceLightYear)*parsecAU, 63241.077084, 1e-6)
+	assertDistanceClose(t, "1 pc in au 参考 206264.806247096", DistanceToParsecs(1, DistanceParsec)*parsecAU, 206264.806247096, 1e-9)
+	assertDistanceClose(t, "648000/pi au in pc", DistanceToParsecs(parsecAU, DistanceAU), 1, 1e-14)
+}
+
+func TestDistanceToParsecsRoundTrip(t *testing.T) {
+	for _, pc := range []float64{0.0001, 1, 2.637, 5.7803, 1000} {
+		assertDistanceClose(t, "pc round trip", DistanceToParsecs(pc, DistanceParsec), pc, 1e-15)
+		ly := pc / testPcPerLy
+		assertDistanceClose(t, "pc->ly->pc", DistanceToParsecs(ly, DistanceLightYear), pc, 1e-12)
+		assertDistanceClose(t, "au round trip", DistanceToParsecs(pc*parsecAU, DistanceAU), pc, 1e-12)
+	}
+}
+
+func TestDistanceToParsecsRejectsInvalidInput(t *testing.T) {
+	for _, value := range []float64{0, -1, math.NaN(), math.Inf(1), math.Inf(-1)} {
+		if got := DistanceToParsecs(value, DistanceParsec); !math.IsNaN(got) {
+			t.Fatalf("DistanceToParsecs(%v, parsec) = %v, want NaN", value, got)
+		}
+	}
+	if got := DistanceToParsecs(1, DistanceUnit(200)); !math.IsNaN(got) {
+		t.Fatalf("DistanceToParsecs(1, unknown unit) = %v, want NaN", got)
+	}
+}