[ty] fix display of top ParamSpec specialization (#22227)

## Summary

I only noticed this in the ecosystem report of
https://github.com/astral-sh/ruff/pull/22213 after merging it. The
change to displaying `Top[]` wrapper around the entire signature instead
of just the parameters had the side effect of not showing it at all when
displaying a top ParamSpec specialization. This PR fixes that.

Marking internal since this is a fixup of a not-released PR.

## Test Plan

Added mdtest that fails without this PR.

crates/ty_python_semantic/resources/mdtest/type_display/callable.md

@@ -1,5 +1,9 @@
 # Display of callable types
 
+## Parenthesizing callables
+
+### Simple
+
 We parenthesize callable types when they appear inside more complex types, to disambiguate:
 
 ```py
@@ -9,11 +13,13 @@ def f(x: Callable[[], str] | Callable[[int], str]):
     reveal_type(x)  # revealed: (() -> str) | ((int, /) -> str)
 ```
 
+### Overloaded
+
 We don't parenthesize display of an overloaded callable, since it is already wrapped in
 `Overload[...]`:
 
 ```py
-from typing import overload
+from typing import overload, Callable
 from ty_extensions import CallableTypeOf
 
 @overload
@@ -28,11 +34,36 @@ def _(flag: bool, c: CallableTypeOf[f]):
     reveal_type(x)  # revealed: Overload[(x: int) -> bool, (x: str) -> str] | Literal[True]
 ```
 
+### Top
+
 And we don't parenthesize the top callable, since it is wrapped in `Top[...]`:
 
 ```py
+from typing import Callable
 from ty_extensions import Top
 
 def f(x: Top[Callable[..., str]] | Callable[[int], int]):
     reveal_type(x)  # revealed: Top[(...) -> str] | ((int, /) -> int)
 ```
+
+## Top ParamSpec
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+We wrap the signature of a top ParamSpec with `Top[...]`:
+
+```py
+from typing import Callable
+
+class C[**P]:
+    def __init__(self, f: Callable[P, object]) -> None:
+        self.f = f
+
+def _(x: object):
+    if callable(x):
+        c = C(x)
+        reveal_type(c)  # revealed: C[Top[(...)]]
+```

crates/ty_python_semantic/src/types/display.rs

@@ -1600,10 +1600,16 @@ impl<'db> FmtDetailed<'db> for DisplayCallableType<'_, 'db> {
         match self.signatures.overloads.as_slice() {
             [signature] => {
                 if matches!(self.kind, CallableTypeKind::ParamSpecValue) {
+                    if signature.parameters().is_top() {
+                        f.write_str("Top[")?;
+                    }
                     signature
                         .parameters()
                         .display_with(self.db, self.settings.clone())
                         .fmt_detailed(f)?;
+                    if signature.parameters().is_top() {
+                        f.write_str("]")?;
+                    }
                 } else {
                     signature
                         .display_with(self.db, self.settings.clone())