feat: 扩展天文计算能力

- 新增日食、月食、本地可见性、中心线、半影区域、SVG 图示与沙罗周期信息
- 新增行星冲合、留、方照、物理星历、视直径、相位、亮肢角、轨道节点等计算
- 新增木星伽利略卫星位置、现象与接触事件计算
- 新增恒星星表、星座判定、自行修正与观测辅助能力
- 新增 coord、formula、orbit、sundial、lite/sun、lite/moon 等扩展包
- 完善农历年号、月相英文别名、视差角、大气质量、折射、日晷与双星计算
- 增加 NASA、JPL Horizons、IMCCE 等回归测试数据与基线测试
- 重构基础算法文件组织，补充大量公开 API 注释和语义回归测试
- 更新中文和英文 README，补充示例、精度说明、SVG 配图

basic/mercury_event_helpers_test.go

@@ -0,0 +1,66 @@
+package basic
+
+import (
+	"math"
+	"time"
+)
+
+type mercuryEventFunc func(float64) float64
+
+type mercuryEventCase struct {
+	name      string
+	tolerance float64
+	fn        mercuryEventFunc
+}
+
+func mercuryEventSamples() []time.Time {
+	start := time.Date(1995, 1, 15, 12, 34, 56, 789000000, time.UTC)
+	samples := make([]time.Time, 0, 96)
+	for i := 0; i < 48; i++ {
+		d := start.AddDate(0, 0, i*137)
+		d = d.Add(time.Duration((i%7)*3)*time.Hour + time.Duration((i%11)*7)*time.Minute + time.Duration((i%13)*11)*time.Second)
+		samples = append(samples, d)
+	}
+	extraStart := start.AddDate(0, 0, 41)
+	for i := 0; i < 48; i++ {
+		d := extraStart.AddDate(0, 0, i*89)
+		d = d.Add(time.Duration((i%5)*7)*time.Hour + time.Duration((i%13)*5)*time.Minute + time.Duration((i%17)*19)*time.Second)
+		samples = append(samples, d)
+	}
+	return samples
+}
+
+func mercuryEventSampleTTJD(date time.Time) float64 {
+	return TD2UT(Date2JDE(date.UTC()), true)
+}
+
+func mercuryEventCases() []mercuryEventCase {
+	const (
+		conjunctionTolerance = 0.00001
+		searchTolerance      = 30.0 / 86400.0
+	)
+	return []mercuryEventCase{
+		{name: "LastMercuryConjunction", tolerance: conjunctionTolerance, fn: LastMercuryConjunction},
+		{name: "NextMercuryConjunction", tolerance: conjunctionTolerance, fn: NextMercuryConjunction},
+		{name: "LastMercuryInferiorConjunction", tolerance: conjunctionTolerance, fn: LastMercuryInferiorConjunction},
+		{name: "NextMercuryInferiorConjunction", tolerance: conjunctionTolerance, fn: NextMercuryInferiorConjunction},
+		{name: "LastMercurySuperiorConjunction", tolerance: conjunctionTolerance, fn: LastMercurySuperiorConjunction},
+		{name: "NextMercurySuperiorConjunction", tolerance: conjunctionTolerance, fn: NextMercurySuperiorConjunction},
+		{name: "LastMercuryRetrograde", tolerance: searchTolerance, fn: LastMercuryRetrograde},
+		{name: "NextMercuryRetrograde", tolerance: searchTolerance, fn: NextMercuryRetrograde},
+		{name: "LastMercuryProgradeToRetrograde", tolerance: searchTolerance, fn: LastMercuryProgradeToRetrograde},
+		{name: "NextMercuryProgradeToRetrograde", tolerance: searchTolerance, fn: NextMercuryProgradeToRetrograde},
+		{name: "LastMercuryRetrogradeToPrograde", tolerance: searchTolerance, fn: LastMercuryRetrogradeToPrograde},
+		{name: "NextMercuryRetrogradeToPrograde", tolerance: searchTolerance, fn: NextMercuryRetrogradeToPrograde},
+		{name: "LastMercuryGreatestElongation", tolerance: searchTolerance, fn: LastMercuryGreatestElongation},
+		{name: "NextMercuryGreatestElongation", tolerance: searchTolerance, fn: NextMercuryGreatestElongation},
+		{name: "LastMercuryGreatestElongationEast", tolerance: searchTolerance, fn: LastMercuryGreatestElongationEast},
+		{name: "NextMercuryGreatestElongationEast", tolerance: searchTolerance, fn: NextMercuryGreatestElongationEast},
+		{name: "LastMercuryGreatestElongationWest", tolerance: searchTolerance, fn: LastMercuryGreatestElongationWest},
+		{name: "NextMercuryGreatestElongationWest", tolerance: searchTolerance, fn: NextMercuryGreatestElongationWest},
+	}
+}
+
+func almostEqualWithinDays(got, want, tolerance float64) bool {
+	return math.Abs(got-want) <= tolerance
+}