feat(tenpayv2): 新增获取仿真测试系统验签密钥接口

src/SKIT.FlurlHttpClient.Wechat.TenpayV2/Models/XDC/GetSandboxSignKeyRequest.cs

@@ -0,0 +1,22 @@
+namespace SKIT.FlurlHttpClient.Wechat.TenpayV2.Models
+{
+    /// <summary>
+    /// <para>表示 [POST] /xdc/apiv2getsignkey/sign/getsignkey 接口的请求。</para>
+    /// </summary>
+    public class GetSandboxSignKeyRequest : WechatTenpaySignableRequest
+    {
+        /// <summary>
+        /// <inheritdoc/>
+        /// </summary>
+        [Newtonsoft.Json.JsonProperty("mch_id")]
+        [System.Text.Json.Serialization.JsonPropertyName("mch_id")]
+        public override string? MerchantId { get; set; }
+
+        /// <summary>
+        /// <inheritdoc/>
+        /// </summary>
+        [Newtonsoft.Json.JsonIgnore]
+        [System.Text.Json.Serialization.JsonIgnore]
+        public override string? AppId { get; set; }
+    }
+}

src/SKIT.FlurlHttpClient.Wechat.TenpayV2/Models/XDC/GetSandboxSignKeyResponse.cs

@@ -0,0 +1,29 @@
+namespace SKIT.FlurlHttpClient.Wechat.TenpayV2.Models
+{
+    /// <summary>
+    /// <para>表示 [POST] /xdc/apiv2getsignkey/sign/getsignkey 接口的响应。</para>
+    /// </summary>
+    public class GetSandboxSignKeyResponse : WechatTenpaySignableResponse
+    {
+        /// <summary>
+        /// <inheritdoc/>
+        /// </summary>
+        [Newtonsoft.Json.JsonProperty("mch_id")]
+        [System.Text.Json.Serialization.JsonPropertyName("mch_id")]
+        public override string? MerchantId { get; set; }
+
+        /// <summary>
+        /// <inheritdoc/>
+        /// </summary>
+        [Newtonsoft.Json.JsonIgnore]
+        [System.Text.Json.Serialization.JsonIgnore]
+        public override string? AppId { get; set; }
+
+        /// <summary>
+        /// 获取或设置沙箱密钥。
+        /// </summary>
+        [Newtonsoft.Json.JsonProperty("sandbox_signkey")]
+        [System.Text.Json.Serialization.JsonPropertyName("sandbox_signkey")]
+        public string SandboxSignKey { get; set; } = default!;
+    }
+}