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

basic/solar_eclipse_central_envelope_test.go

@@ -0,0 +1,102 @@
+package basic
+
+import (
+	"math"
+	"testing"
+)
+
+func TestSolarEclipse20120521CentralBandIsContinuousCriticalEnvelope(t *testing.T) {
+	seed := JDECalc(2012, 5, 21)
+	result := SolarEclipsePartialFootprints(seed, SolarEclipsePartialFootprintOptions{
+		StepDays: 2.0 / 1440.0, BoundaryPoints: 96,
+	})
+	if result.Eclipse.Type != SolarEclipseAnnular ||
+		result.Eclipse.Centrality != SolarEclipseCentralTwoLimits {
+		t.Fatalf("eclipse=%s/%s, want two-limit annular", result.Eclipse.Type, result.Eclipse.Centrality)
+	}
+	if len(result.CentralBandSegments) != 1 {
+		t.Fatalf("central-band segments=%d, want one continuous envelope", len(result.CentralBandSegments))
+	}
+
+	ring := result.CentralBandSegments[0]
+	if len(ring) < 4 || solarEclipsePathDistanceKM(ring[0], ring[len(ring)-1]) > 0.01 {
+		t.Fatal("central-band envelope is not closed")
+	}
+	solver := newSolarEclipseSolver(CalcMoonSHByJDE(seed, 0), SolarEclipseModelNASABulletinSplitK)
+	interiorPoints := 0
+	for index, point := range ring {
+		if index > 0 {
+			if distance := solarEclipsePathDistanceKM(ring[index-1], point); distance >
+				solarEclipseCentralEnvelopeMaxSpacingKM+1e-6 {
+				t.Fatalf("central-band edge %d is %.3f km, want at most %.3f km",
+					index-1, distance, solarEclipseCentralEnvelopeMaxSpacingKM)
+			}
+		}
+		if solarEclipseCentralEnvelopePointOnHorizonClosure(
+			point, result.CentralBandHorizonClosures,
+		) {
+			continue
+		}
+		residual, ok := solarEclipseNonCentralBandBoundaryResidualAt(
+			solver.magnitudeEvaluationAt(point.JDE), point.Longitude, point.Latitude,
+		)
+		if !ok || math.Abs(residual[0]) > 1e-6 ||
+			math.Abs(residual[1]) > solarEclipseNonCentralBandDerivativeTolerance {
+			t.Fatalf("central-band point %d altitude=%g residual=(%g,%g), want critical-envelope solution",
+				index, point.SunAltitude, residual[0], residual[1])
+		}
+		interiorPoints++
+	}
+	if interiorPoints < 100 {
+		t.Fatalf("critical-envelope points=%d, want a densely sampled continuous boundary", interiorPoints)
+	}
+
+	// NADC 3D eclipse data publishes these samples on the two 2012 central
+	// limits. The allowance covers ephemeris/delta-T model differences and the
+	// finite spacing between our continuation samples.
+	for _, anchor := range []struct {
+		name  string
+		point SolarEclipsePathPoint
+	}{
+		{name: "north limit", point: SolarEclipsePathPoint{Longitude: 120.9238, Latitude: 24.6531}},
+		{name: "south limit", point: SolarEclipsePathPoint{Longitude: 120.3071, Latitude: 27.5328}},
+	} {
+		nearest := math.Inf(1)
+		for _, point := range ring {
+			nearest = math.Min(nearest, solarEclipsePathDistanceKM(point, anchor.point))
+		}
+		if nearest > 60 {
+			t.Fatalf("central-band %s is %.3f km from the NADC reference sample", anchor.name, nearest)
+		}
+	}
+}
+
+func TestSolarEclipseCentralEnvelopeIndependentOfRiseSetOutput(t *testing.T) {
+	seed := JDECalc(2012, 5, 21)
+	withCurves := SolarEclipsePartialFootprints(seed, SolarEclipsePartialFootprintOptions{StepDays: 2.0 / 1440, BoundaryPoints: 96})
+	withoutCurves := SolarEclipsePartialFootprints(seed, SolarEclipsePartialFootprintOptions{StepDays: 2.0 / 1440, BoundaryPoints: 96, DisableRiseSetCurves: true})
+	if len(withoutCurves.CentralBandSegments) == 0 {
+		t.Fatal("disabling output curves removed the authoritative central envelope")
+	}
+	if len(withoutCurves.RiseSetCurves) != 0 {
+		t.Fatal("disabled rise/set curves were returned")
+	}
+	if len(withCurves.CentralBandSegments) != len(withoutCurves.CentralBandSegments) {
+		t.Fatalf("central envelope segment count changed: %d vs %d", len(withCurves.CentralBandSegments), len(withoutCurves.CentralBandSegments))
+	}
+}
+
+func solarEclipseCentralEnvelopePointOnHorizonClosure(
+	point SolarEclipsePathPoint,
+	closures [][]SolarEclipsePathPoint,
+) bool {
+	for _, closure := range closures {
+		for _, horizonPoint := range closure {
+			if solarEclipsePathDistanceKM(point, horizonPoint) <= 0.001 &&
+				math.Abs(point.JDE-horizonPoint.JDE) <= solarEclipsePathDuplicateTimeDays {
+				return true
+			}
+		}
+	}
+	return false
+}