fix: StandardCharsets.UTF_8 替换为 Charset.forName("UTF-8")

Android 4.2（API 17）不支持 java.nio.charset.StandardCharsets（API 19+），
5 个文件统一改用兼容 API 1 的 String 重载：
- DeviceIdentityProvider / HMacShaUtils / Md5Utils: Charset.forName
- UrlParamBuilder: URLEncoder.encode(str, "UTF-8")
- ContentDetailUtils: 删除未使用的 import

libcore/src/main/java/com/pukka/libcore/cipher/HMacShaUtils.java

@@ -1,6 +1,6 @@
 package com.pukka.libcore.cipher;
 
-import java.nio.charset.StandardCharsets;
+import java.nio.charset.Charset;
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
 
@@ -29,7 +29,7 @@ public class HMacShaUtils {
             SecretKeySpec signingKey = new SecretKeySpec(key.getBytes(), HMAC_SHA256_ALGORITHM);
             Mac mac = Mac.getInstance(HMAC_SHA256_ALGORITHM);
             mac.init(signingKey);
-            return mac.doFinal(data.getBytes(StandardCharsets.UTF_8));
+            return mac.doFinal(data.getBytes(Charset.forName("UTF-8")));
         } catch (NoSuchAlgorithmException e) {
             e.printStackTrace();
         } catch (InvalidKeyException e) {
@@ -51,7 +51,7 @@ public class HMacShaUtils {
             SecretKeySpec signingKey = new SecretKeySpec(key.getBytes(), HMAC_SHA1_ALGORITHM);
             Mac mac = Mac.getInstance(HMAC_SHA1_ALGORITHM);
             mac.init(signingKey);
-            return mac.doFinal(data.getBytes(StandardCharsets.UTF_8));
+            return mac.doFinal(data.getBytes(Charset.forName("UTF-8")));
         } catch (Exception ex) {
             ex.printStackTrace();
         }

libcore/src/main/java/com/pukka/libcore/cipher/Md5Utils.java

@@ -2,7 +2,7 @@ package com.pukka.libcore.cipher;
 
 import com.pukka.libcore.utils.ByteConversionUtils;
 
-import java.nio.charset.StandardCharsets;
+import java.nio.charset.Charset;
 import java.security.MessageDigest;
 
 /**
@@ -61,7 +61,7 @@ public class Md5Utils {
     public static String encrypt(String message) {
         String md5str = "";
         try {
-            md5str = encrypt(message.getBytes(StandardCharsets.UTF_8));
+            md5str = encrypt(message.getBytes(Charset.forName("UTF-8")));
         } catch (Exception e) {
             e.printStackTrace();
         }