Add LocalDetachedExecutor

[bruno-f-cruz]

Adds LocalDetachedExecutor, a fire-and-forget Executor implementation that spawns a subprocess via subprocess.Popen and returns immediately without waiting for it to complete.

Design:

• Implements the existing Executor protocol — no new interface required
• stdout/stderr redirected to DEVNULL (no dangling pipe handles)
• shell=False enforced
• Returns a placeholder CommandResult(stdout=None, stderr=None, exit_code=0) immediately; callers must not rely on it to reflect actual process outcome
• Exported from clabe.apps

Usage:

from clabe.apps import LocalDetachedExecutor

executor = LocalDetachedExecutor()
executor.run(app.command)  # spawns process, returns immediately