feat: ✨ 新增string扩展函数 IsJsonString (#19)

Co-authored-by: tk <fiyne1a@dingtalk.com>

src/backend/NSExt.Tests/AllTests.cs

@@ -0,0 +1,19 @@
+using NSExt.Extensions;
+using Xunit;
+
+namespace NSExt;
+
+/// <summary>
+///     所有测试用例
+/// </summary>
+public class AllTests
+{
+    /// <summary>
+    ///     IsJsonString
+    /// </summary>
+    [Fact]
+    public void IsJsonString()
+    {
+        Assert.True("{\"a\":\"b\"}".IsJsonString());
+    }
+}