Hide subprocess terminal for Windows system

[MrYangxf]

Issue

When spawn Claude subprocess via SDK on Windows, a terminal window remains visible. Need to hide the terminal for a cleaner UX.

Workaround

before

claude-agent-sdk-python/src/claude_agent_sdk/_internal/transport/subprocess_cli.py

Lines 403 to 411 in 7866e5f

	self._process = await anyio.open_process(
	cmd,
	stdin=PIPE,
	stdout=PIPE,
	stderr=stderr_dest,
	cwd=self._cwd,
	env=process_env,
	user=self._options.user,
	)

after

if sys.platform == "win32":
    import subprocess
    creationflags = subprocess.CREATE_NO_WINDOW

self._process = await anyio.open_process(
    cmd,
    stdin=PIPE,
    stdout=PIPE,
    stderr=stderr_dest,
    cwd=self._cwd,
    env=process_env,
    user=self._options.user,
    creationflags=creationflags if creationflags else 0
)