fix: preserve annotation metadata when cloning wrapped partials

Addresses Codex P1: when reconstructing a partial to strip __wrapped__,
copy over functools.WRAPPER_ASSIGNMENTS (__module__, __qualname__, etc.)
so deferred annotation resolution works correctly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

fastmcp_slim/fastmcp/utilities/callable_utils.py

@@ -66,7 +66,21 @@ def prepare_callable(fn: Callable[..., Any]) -> Callable[..., Any]:
     # Strip __wrapped__ from partials so Pydantic sees the partial's own
     # signature with bound args removed, not the original function's signature.
     if isinstance(fn, functools.partial) and hasattr(fn, "__wrapped__"):
+        old = fn
         fn = functools.partial(fn.func, *fn.args, **fn.keywords)
+        # Preserve annotation metadata copied by functools.update_wrapper
+        # (e.g. __module__, __qualname__) needed for deferred annotation
+        # resolution when `from __future__ import annotations` is active.
+        for attr in functools.WRAPPER_ASSIGNMENTS:
+            try:
+                val = getattr(old, attr)
+            except AttributeError:
+                pass
+            else:
+                try:
+                    setattr(fn, attr, val)
+                except AttributeError:
+                    pass
 
     # Callable classes (not routines, not partials) → unwrap to __call__
     if not inspect.isroutine(fn) and not isinstance(fn, functools.partial):