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/src/tools/semantic_tokens.py

@@ -7,6 +7,23 @@ from common.load_data import standard_items
 import lsprotocol.types as lsp
 
 
+# Constructing a PluginManager scans entry points, and get_commands() rebuilds
+# the builtin command set on every call. Semantic tokens are requested often, so
+# cache the manager and the resolved commands per plugin set.
+_PLUGIN_MANAGER = None
+_COMMANDS_CACHE = {}
+
+
+def _load_commands(plugins):
+    global _PLUGIN_MANAGER
+    if _PLUGIN_MANAGER is None:
+        _PLUGIN_MANAGER = PluginManager()
+    key = tuple(plugins)
+    if key not in _COMMANDS_CACHE:
+        _COMMANDS_CACHE[key] = _PLUGIN_MANAGER.get_commands(list(plugins))
+    return _COMMANDS_CACHE[key]
+
+
 class TokenModifier(enum.IntFlag):
     deprecated = enum.auto()
     readonly = enum.auto()
@@ -47,7 +64,7 @@ TOKEN_TYPES = [
 
 class _Highlighter(Visitor):
     def __init__(self, plugins, custom_functions: dict[str : list[lsp.CompletionItem]]):
-        self._commands = PluginManager().get_commands(plugins)
+        self._commands = _load_commands(plugins)
         self._tokens = []
         self.custom_functions = custom_functions