feat: unify name demangling with single Lean implementation

script/profiler/lean_demangle_cli.lean

@@ -0,0 +1,32 @@
+/-
+Copyright (c) 2026 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison
+-/
+module
+
+import Lean.Compiler.NameDemangling
+
+/-!
+Lean name demangler CLI tool. Reads mangled symbol names from stdin (one per
+line) and writes demangled names to stdout. Non-Lean symbols pass through
+unchanged. Like `c++filt` but for Lean names.
+
+Usage:
+    echo "l_Lean_Meta_foo" | lean --run lean_demangle_cli.lean
+    cat symbols.txt | lean --run lean_demangle_cli.lean
+-/
+
+open Lean.Name.Demangle
+
+def main : IO Unit := do
+  let stdin ← IO.getStdin
+  let stdout ← IO.getStdout
+  repeat do
+    let line ← stdin.getLine
+    if line.isEmpty then break
+    let sym := line.trimRight
+    match demangleSymbol sym with
+    | some s => stdout.putStrLn s
+    | none => stdout.putStrLn sym
+    stdout.flush