Add experimental VS Code (code) runtime to juv run

This PR adds a `code` runtime option to `juv run`, allowing VS Code to
be launched in a way similar to other Jupyter runtimes. The approach
uses the behavior of the `code` CLI, which inherits the environment
it was run in.

A script is created using the inline metadata so that running `code
<notebook.ipynb>` ensures a virtual environment is available in the VS
Code session with the necessary dependencies.

Ideally, we'd have a VS Code extension to dynamically create and
register virtual environments for better discoverability. This
implementation goes the other way by enabling basic support via the CLI.
However, the user must manually select the virtual environment from VS
Code's dropdown, where it appears with an obscure, temporary name
(derived from the hashed environment created by `uv`).

src/juv/_run.py

@@ -83,7 +83,7 @@ def run(  # noqa: PLR0913
     if mode == "dry":
         print(f"uv {' '.join(args)}")  # noqa: T201
 
-    elif mode == "managed":
+    elif mode == "managed" and runtime.name != "code":
         from ._run_managed import run as run_managed
 
         run_managed(script, args, str(path))

src/juv/_run_template.py

@@ -6,11 +6,11 @@
 if typing.TYPE_CHECKING:
     import pathlib
 
-RuntimeName = typing.Literal["notebook", "lab", "nbclassic"]
+RuntimeName = typing.Literal["notebook", "lab", "nbclassic", "code"]
 
 
 def is_notebook_kind(kind: str) -> typing.TypeGuard[RuntimeName]:
-    return kind in {"notebook", "lab", "nbclassic"}
+    return kind in {"notebook", "lab", "nbclassic", "code"}
 
 
 @dataclass
@@ -45,12 +45,19 @@ def script_template(self) -> str:
             return NOTEBOOK
         if self.name == "nbclassic":
             return NBCLASSIC
+        if self.name == "code":
+            return VSCODE
         msg = f"Invalid self: {self.name}"
         raise ValueError(msg)
 
     def as_with_arg(self) -> str:
-        # lab is actually jupyterlab
-        with_ = "jupyterlab" if self.name == "lab" else self.name
+        with_ = {
+            "lab": "jupyterlab",
+            "notebook": "notebook",
+            "nbclassic": "nbclassic",
+            # vscode needs ipykernel to be in the environment
+            "code": "ipykernel",
+        }[self.name]
 
         # append version if present
         if self.version:
@@ -200,6 +207,14 @@ def handle_termination(signum, frame):
 main()
 """
 
+VSCODE = """
+{meta}
+import subprocess
+import os
+
+subprocess.run(["code", r"{notebook}"], check=True, env=os.environ)
+"""
+
 
 def prepare_run_script_and_uv_run_args(  # noqa: PLR0913
     *,