feat(scripts): add typed Parameters.Get<T>() helpers for script API

Replace raw dictionary casting with ScriptParameters wrapper that provides
Get<T>, Get<T?>, Get<T[]>, and Get<List<T>> with clear error messages,
numeric conversion, and JsonElement support for Inbound API parameters.

tests/ScadaLink.SiteRuntime.Tests/Scripts/SandboxTests.cs

@@ -1,4 +1,5 @@
 using Microsoft.Extensions.Logging.Abstractions;
+using ScadaLink.Commons.Types;
 using ScadaLink.SiteRuntime.Scripts;
 
 namespace ScadaLink.SiteRuntime.Tests.Scripts;
@@ -236,7 +237,7 @@ public class SandboxTests
         var globals = new ScriptGlobals
         {
             Instance = null!,
-            Parameters = new Dictionary<string, object?>(),
+            Parameters = new ScriptParameters(),
             CancellationToken = cts.Token
         };
 
@@ -266,7 +267,7 @@ public class SandboxTests
         var globals = new ScriptGlobals
         {
             Instance = null!,
-            Parameters = new Dictionary<string, object?>(),
+            Parameters = new ScriptParameters(),
             CancellationToken = cts.Token
         };