fix(python): Sandbox.hibernate and Sandbox.shutdown classmethod shadows instance method

[Dev-X25874]

In Python, a @classmethod defined after an instance method of the same name
silently replaces it in the class __dict__. The Sandbox class defined
async def hibernate(self) and async def shutdown(self) as instance methods,
then redefined both as @classmethod factories further down in the same class
body. The classmethods won, making the instance methods unreachable.

Any call to await sandbox.hibernate() or await sandbox.shutdown() on a live
Sandbox instance dispatched to the classmethod, which then raised:

TypeError: hibernate() missing 1 required positional argument: 'sandbox_id'

The TypeScript SDK avoids this naturally — static and instance methods occupy
separate namespaces. Python has no equivalent distinction, so the two classmethod
factories are renamed to hibernate_by_id / shutdown_by_id.

• await sandbox.hibernate() — instance method, restored ✓
• await sandbox.shutdown() — instance method, restored ✓
• await Sandbox.hibernate_by_id("id", api_key=...) — classmethod factory ✓
• await Sandbox.shutdown_by_id("id", api_key=...) — classmethod factory ✓

Adds TestSandboxLifecycleMethods in tests/test_utils.py using
inspect.getattr_static to assert the resolution at class-definition time,
so this can never silently regress again.