Add SPC provider parsing helpers

internal/providers/spc/time.go

@@ -0,0 +1,24 @@
+package spc
+
+import (
+	"strings"
+	"time"
+)
+
+// ParseISOTimestamp parses SPC ISO timestamps from GeoJSON properties.
+func ParseISOTimestamp(value string) (time.Time, error) {
+	return time.Parse(time.RFC3339, strings.TrimSpace(value))
+}
+
+func parseOptionalISOTimestamp(value string) *time.Time {
+	value = strings.TrimSpace(value)
+	if value == "" {
+		return nil
+	}
+	t, err := ParseISOTimestamp(value)
+	if err != nil {
+		return nil
+	}
+	tt := t.UTC()
+	return &tt
+}