feat: 增强日月食搜索、沙罗周期与内行星凌日

- 使用压缩表加速查找日月食沙罗周期信息
- 优化日月食搜索跳步，减少非食季朔望月扫描
- 新增本地日全食、日环食、月全食搜索接口，返回 ok 区分未找到结果
- 新增水星、金星地心凌日查询及测试

venus/transit_test.go

@@ -0,0 +1,23 @@
+package venus
+
+import (
+	"testing"
+	"time"
+)
+
+func TestTransitWrappers(t *testing.T) {
+	loc := time.FixedZone("CST", 8*3600)
+	info := NextTransit(time.Date(2012, 1, 1, 0, 0, 0, 0, loc))
+	if !info.Valid {
+		t.Fatal("expected valid transit")
+	}
+	if info.Greatest.Location() != loc {
+		t.Fatalf("timezone mismatch: got %v want %v", info.Greatest.Location(), loc)
+	}
+	if info.Greatest.Year() != 2012 || info.Greatest.Month() != time.June || info.Greatest.Day() != 6 {
+		t.Fatalf("unexpected greatest time: %s", info.Greatest)
+	}
+	if !info.HasInternal || info.Duration <= 0 || info.InternalDuration <= 0 {
+		t.Fatalf("unexpected durations: %+v", info)
+	}
+}