feat: 引入可切换星历模型并扩展天象观测链路

- 新增半解析、旧模型、自定义与多源堆叠星历实例，提供 Context、Instance、SPK 读取及状态与视位置计算
- 统一太阳、月球和行星实例接口，扩展黄经穿越、留、相位、最近角距、偕日可见、任意高度升落、轨道节点及凌日等天象查询
- 完善日月食、月掩与凌日的月缘剖面、有限盘面接触、站心修正、局地可见性、全球路径和地图输出
- 新增 SVG、GeoJSON、KML 天象输出及凌日、月掩和月缘地形相关缓存与几何求解
- 新增恒星星表导入与查询，支持 CSV、Hipparcos、BSC5、Stellarium 等格式及名称、交叉标识、锥面检索和星等过滤
- 补充 IAU 2006、地球定向、折射消光、大气观测、轨道传播及半解析行星/月球数据支持
- 将默认未来民用时标切换为 TimeScaleLeapHour，更新 2027–2400 农历速查表、中文日期解析和时区边界处理
- 增加事件基线、跨模型回归、几何边界、月缘地形和输出契约测试，完善中英文手册、示例资源、NOTICE 与忽略规则

planet/spk/guard_test.go

@@ -0,0 +1,84 @@
+// 被测契约：畸形阶数与非有限系数报 ErrInvalidFile 而不是 panic 或返回 NaN；无关段的覆盖缺口不阻断有效路径。
+package spk
+
+import (
+	"encoding/binary"
+	"errors"
+	"math"
+	"testing"
+
+	"b612.me/astro/internal/ephem"
+)
+
+func type21Record(maxdim, kqmax1, kq int) []float64 {
+	record := make([]float64, 4*maxdim+12)
+	record[0] = float64(maxdim)
+	for index := 0; index < maxdim; index++ {
+		record[2+index] = 1
+	}
+	record[4*maxdim+8] = float64(kqmax1)
+	for component := 0; component < 3; component++ {
+		record[4*maxdim+9+component] = float64(kq)
+	}
+	return record
+}
+
+func TestType21RejectsInconsistentOrders(t *testing.T) {
+	cases := []struct{ maxdim, kqmax1, kq int }{
+		{15, 3, 15},
+		{15, 27, 1},
+		{15, 17, 1},
+		{15, 5, 5},
+	}
+	for _, c := range cases {
+		_, _, err := evaluateType21(0, type21Record(c.maxdim, c.kqmax1, c.kq))
+		if !errors.Is(err, ErrInvalidFile) {
+			t.Errorf("maxdim=%d kqmax1=%d kq=%d: err = %v, want %v", c.maxdim, c.kqmax1, c.kq, err, ErrInvalidFile)
+		}
+	}
+	if _, _, err := evaluateType21(0, type21Record(15, 16, 15)); err != nil {
+		t.Errorf("maximal valid orders: err = %v", err)
+	}
+}
+
+func TestType21RejectsNonFiniteRecord(t *testing.T) {
+	record := type21Record(15, 3, 1)
+	record[15+2] = math.NaN()
+	if _, _, err := evaluateType21(0, record); !errors.Is(err, ErrInvalidFile) {
+		t.Errorf("err = %v, want %v", err, ErrInvalidFile)
+	}
+}
+
+func TestType2RejectsNonFiniteCoefficient(t *testing.T) {
+	path := writeTestSPK(t, binary.LittleEndian, "LTL-IEEE",
+		testSPKSegment{target: Mars, center: Sun, frame: 1, typ: 2, start: 0, end: 10, words: type2Words(0, 10, []float64{5, 5, math.NaN(), 20, 30})},
+	)
+	file, err := Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+	if _, _, err := file.State(Mars, Sun, spkJ2000+5/spkSecondsDay); !errors.Is(err, ErrInvalidFile) {
+		t.Errorf("err = %v, want %v", err, ErrInvalidFile)
+	}
+}
+
+func TestUnrelatedSegmentCoverageDoesNotBlockDirectPath(t *testing.T) {
+	path := writeTestSPK(t, binary.LittleEndian, "LTL-IEEE",
+		testSPKSegment{target: Mars, center: Sun, frame: 1, typ: 2, start: 0, end: 10, words: type2Words(0, 10, []float64{5, 5, 10, 20, 30})},
+		testSPKSegment{target: Sun, center: SSB, frame: 1, typ: 2, start: 100, end: 110, words: type2Words(100, 10, []float64{105, 5, 1, 2, 3})},
+	)
+	file, err := Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+	pos, _, err := file.State(Mars, Sun, spkJ2000+5/spkSecondsDay)
+	if err != nil {
+		t.Fatalf("Mars→Sun err = %v", err)
+	}
+	assertVector(t, pos, [3]float64{10, 20, 30})
+	if _, _, err := file.State(Mars, SSB, spkJ2000+5/spkSecondsDay); err != ephem.ErrOutOfRange {
+		t.Errorf("Mars→SSB err = %v, want %v", err, ephem.ErrOutOfRange)
+	}
+}