fix(rawcli): friendly message when prompt_toolkit isn't installed

`pm3py rawcli` lives behind the optional [rawcli] extra; a plain install
of pm3py doesn't pull prompt_toolkit. Catch the ModuleNotFoundError and
print an install hint (pip install 'pm3py[rawcli]') with exit code 2,
instead of dumping a traceback.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pm3py/cli/main.py

@@ -6,6 +6,7 @@ is left for ``flash`` (wrapping pm3flash) and a future ``client`` command CLI.
 from __future__ import annotations
 
 import argparse
+import sys
 
 
 def build_parser() -> argparse.ArgumentParser:
@@ -20,6 +21,16 @@ def main(argv: list[str] | None = None) -> int:
     parser = build_parser()
     args = parser.parse_args(argv)
     if args.command == "rawcli":
+        try:
+            import prompt_toolkit  # noqa: F401
+        except ModuleNotFoundError:
+            print(
+                "pm3py rawcli needs prompt_toolkit, which isn't installed.\n"
+                "  install it with:  pip install 'pm3py[rawcli]'\n"
+                "  or directly:      pip install prompt_toolkit",
+                file=sys.stderr,
+            )
+            return 2
         from pm3py.cli.rawcli.app import run
         return run(port=args.port)
     parser.print_help()