fix(stringutil): use InvariantCulture for byte-size formatting

Locale-Bug: BytesToString rendert auf deutscher Locale "1,5GB" statt
"1.5GB". InvariantCulture pinnt den Dezimal-Separator. Plus
InternalsVisibleTo-Hook für ein lokales (gitignored) Test-Projekt.

.gitignore

@@ -11,6 +11,10 @@
 .vscode/
 scripts/
 
+# Local test project (stays out of the published plugin repo;
+# pure-function safety net for refactor cycles)
+HellionChat.Tests/
+
 # Packaging
 pack/
 

HellionChat.sln

@@ -1,16 +1,31 @@
-
+
 Microsoft Visual Studio Solution File, Format Version 12.00
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HellionChat", "HellionChat\HellionChat.csproj", "{739F75E6-B65F-41EF-9D90-F7BC519E4875}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
+		Debug|x64 = Debug|x64
+		Debug|x86 = Debug|x86
 		Release|Any CPU = Release|Any CPU
+		Release|x64 = Release|x64
+		Release|x86 = Release|x86
 	EndGlobalSection
 	GlobalSection(ProjectConfigurationPlatforms) = postSolution
 		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Debug|x64.Build.0 = Debug|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Debug|x86.Build.0 = Debug|Any CPU
 		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Release|Any CPU.Build.0 = Release|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Release|x64.ActiveCfg = Release|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Release|x64.Build.0 = Release|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Release|x86.ActiveCfg = Release|Any CPU
+		{739F75E6-B65F-41EF-9D90-F7BC519E4875}.Release|x86.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
 	EndGlobalSection
 EndGlobal

HellionChat/HellionChat.csproj

@@ -36,6 +36,13 @@
         <PackageReference Include="SixLabors.ImageSharp" Version="[3.1.12, 4.0.0)" />
     </ItemGroup>
 
+    <ItemGroup>
+        <!-- Pure-function test suites in HellionChat.Tests need access to
+             the internal helper classes (StringUtil, UriPayload, Tokenizer
+             etc.). Test assembly does not get redistributed. -->
+        <InternalsVisibleTo Include="HellionChat.Tests" />
+    </ItemGroup>
+
     <ItemGroup>
         <Compile Update="Resources\Language.Designer.cs">
             <DesignTime>True</DesignTime>

HellionChat/Util/StringUtil.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using System.Text;
 
 namespace HellionChat.Util;
@@ -24,7 +25,8 @@ internal static class StringUtil
         var place = Convert.ToInt32(Math.Floor(Math.Log(bytes, 1024)));
         var num = Math.Round(bytes / Math.Pow(1024, place), 1);
         // "0.#" keeps the rounded fractional digit (1.5 GB stays "1.5GB"); "N0"
-        // would truncate it back to integer.
-        return (Math.Sign(byteCount) * num).ToString("0.#") + suf[place];
+        // would truncate it back to integer. InvariantCulture pins the decimal
+        // separator to '.' so a German locale doesn't render "1,5GB".
+        return (Math.Sign(byteCount) * num).ToString("0.#", CultureInfo.InvariantCulture) + suf[place];
     }
 }