Delegate TCL folding to server, fix bugs, and enhance stability

- Move TCL folding range computation from client to language server, avoiding duplicate regions.
- Serialize language server restarts to prevent multiple server instances running concurrently.
- Pin server-side Python dependencies to specific minor versions for improved stability and predictability.
- Make debug server connection non-fatal, allowing the language server to start even if the debugger isn't attached.
- Optimize semantic token generation by caching Tclint plugin commands.

server/pyproject.toml

@@ -4,9 +4,12 @@ version = "0.1.0"
 description = "Python language server for NX Postprocessor Support"
 requires-python = ">=3.8"
 dependencies = [
-    "pygls",
-    "packaging",
-    "tclint",
+    # Upper bounds guard against breaking API changes in bundled deps. The code
+    # is written against tclint 0.8.x (see tools/semantic_tokens.py); pin it so a
+    # re-bundle can't silently pull an incompatible major/minor.
+    "pygls>=1.3,<2",
+    "packaging>=24,<27",
+    "tclint>=0.8,<0.9",
 ]
 
 [dependency-groups]