feat: 完善日月食与月掩几何链路并扩展历法接口

- 新增日月食中心带、偏食带、阴影足迹、等时线、食分线及升落边界计算，支持极区与混合食拓扑
- 新增日食单时刻阴影求解器、站心状态查询、批量采样和 ΔT 覆盖接口
- 重构恒星与行星月掩路径，补充有限盘面接触、站心修正、掩带宽度、极区投影及升落边界
- 扩展 SVG 与 GeoJSON 输出，支持详细面板、全球/极区/地球投影、边界闭合、时间标记和拓扑签名
- 扩展日月食候选搜索、局地搜索、沙罗序列预计算与范围外推，补充系列锚点和成员一致性校验
- 补齐古历纪年、儒略历独有闰日、多公历候选、历法改革跨日及精确日期运算接口
- 优化 ΔT、章动、恒星时、月球地平线、事件根搜索和本地星历缓存，降低重复计算开销并提升边界稳定

eclipse/svg/solar_map_partial_sweep_test.go

@@ -0,0 +1,47 @@
+package svg
+
+import (
+	"testing"
+	"time"
+)
+
+// 偏食足迹扫描的密步长请求被夹到两分钟：并集需要一整条自洽的扫描序列，
+// 更密的扫描成倍放大成本却不改产物，事后抽稀又会破坏并集的覆盖面判定。
+func TestSolarEclipseMapPartialStepUsesDefaultSweep(t *testing.T) {
+	date := time.Date(2024, time.April, 8, 0, 0, 0, 0, time.UTC)
+	for _, test := range []struct {
+		requested time.Duration
+		want      time.Duration
+	}{
+		{requested: 0, want: 2 * time.Minute},
+		{requested: -time.Minute, want: 2 * time.Minute},
+		{requested: time.Second, want: 2 * time.Minute},
+		{requested: 10 * time.Second, want: 2 * time.Minute},
+		{requested: time.Minute, want: 2 * time.Minute},
+		{requested: 119 * time.Second, want: 2 * time.Minute},
+		{requested: 2 * time.Minute, want: 2 * time.Minute},
+		{requested: 3 * time.Minute, want: 3 * time.Minute},
+		{requested: 10 * time.Minute, want: 10 * time.Minute},
+	} {
+		got := normalizeSolarEclipseMapSVGOptions(date, SolarEclipseMapSVGOptions{
+			PartialStep: test.requested,
+		}).PartialStep
+		if got != test.want {
+			t.Fatalf("PartialStep %s normalized to %s, want %s", test.requested, got, test.want)
+		}
+	}
+
+	// 一秒请求与默认两分钟请求必须逐字节相同，代价也回到默认量级。
+	fast, fastOK := SolarEclipseMapSVG(date, SolarEclipseMapSVGOptions{
+		Width: 900, Height: 620, Location: time.UTC, PartialStep: time.Second,
+	})
+	defaulted, defaultOK := SolarEclipseMapSVG(date, SolarEclipseMapSVGOptions{
+		Width: 900, Height: 620, Location: time.UTC, PartialStep: 2 * time.Minute,
+	})
+	if !fastOK || !defaultOK {
+		t.Fatal("missing 2024-04-08 map")
+	}
+	if fast != defaulted {
+		t.Fatalf("a one-second sweep request changed the rendered document (%d vs %d bytes)", len(fast), len(defaulted))
+	}
+}