fix(lsp): disambiguate Path reference after pathlib module merge

Fully qualify System.IO.Path.GetFullPath to avoid ambiguity with
Sharpy.Path class added in the pathlib module on dev.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: antonsynd

src/Sharpy.Lsp/SharplyWorkspace.cs

@@ -323,7 +323,7 @@ private void InvalidateDependents(string uri)
 
     private static string FilePathToUri(string filePath)
     {
-        var fullPath = Path.GetFullPath(filePath);
+        var fullPath = System.IO.Path.GetFullPath(filePath);
         return new Uri(fullPath).ToString();
     }