Migrates to .slnx solution format

Updates the solution file format to .slnx.

This change ensures better compatibility with newer versions of Visual Studio and improves the overall solution structure.

Author: niemyjski

.gitattributes

@@ -20,8 +20,8 @@
 *.cmd text
 *.coffee text
 *.config text
-*.cs text diff=csharp 
-*.csproj text merge=union 
+*.cs text diff=csharp
+*.csproj text merge=union
 *.css text
 *.cshtml text
 *.htm text
@@ -37,8 +37,8 @@
 *.txt text
 *.vb text
 *.vbhtml text
-*.vbproj text merge=union 
+*.vbproj text merge=union
 *.xml text
 *.xunit text
 
-*.sln text eol=crlf merge=union 
+*.slnx text eol=crlf merge=union

Exceptionless.DateTimeExtensions.sln

@@ -0,0 +1,9 @@
+<Solution>
+  <Folder Name="/Solution Items/">
+    <File Path=".github/workflows/build.yml" />
+    <File Path="build/common.props" />
+    <File Path="README.md" />
+  </Folder>
+  <Project Path="src/Exceptionless.DateTimeExtensions/Exceptionless.DateTimeExtensions.csproj" />
+  <Project Path="tests/Exceptionless.DateTimeExtensions.Tests/Exceptionless.DateTimeExtensions.Tests.csproj" />
+</Solution>