[Commands] Add STRLEN

Sources/RediStack/Commands/StringCommands.swift

@@ -222,6 +222,12 @@ extension RedisCommand {
         ]
         return .init(keyword: "SETNX", arguments: args)
     }
+  
+  ///[STRLEN](https://redis.io/commands/strln)
+  /// - Parameter key: The key to fetch the length of.
+  public static func strln(_ key: RedisKey) -> RedisCommand<Int> {
+    .init(keyword: "STRLEN", arguments: [.init(from: key)])
+  }
 }
 
 // MARK: -

Tests/RediStackIntegrationTests/Commands/StringCommandsTests.swift

@@ -229,4 +229,10 @@ final class StringCommandsTests: RediStackIntegrationTestCase {
         result = try connection.send(.decrby(#function, by: 0)).wait()
         XCTAssertEqual(result, 7)
     }
+  
+    func test_strlen() throws {
+        XCTAssertNoThrow(try connection.set(#function, to: "value").wait())
+        let val = try connection.send(.strln(#function)).wait()
+        XCTAssertEqual(val, 5)
+    }
 }