fix(device): Device.from_str crashes on a multi-colon device string

[devteamaegis]

What's broken

_split_device_string unpacks string.split(":") into exactly two variables with no maxsplit. A device string with a second colon raises an uncaught error through the public Device.from_str:

>>> from haystack.utils.device import Device
>>> Device.from_str("cuda:0:1")
ValueError: too many values to unpack (expected 2)

Why it happens

str.split(":") without maxsplit=1 returns more than two parts when the string has more than one colon.

Fix

Use split(":", maxsplit=1). "cuda:0:1" then splits to ("cuda", "0:1"); int("0:1") fails and raises the function's existing, descriptive ValueError("Device id must be an integer, got 0:1") instead of the opaque unpack error.

Test

Added a case asserting Device.from_str("cuda:0:1") raises ValueError about the device id; "cuda:0" and "cpu" still parse correctly.

Fixes #11518

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[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/utils
device.py
Project Total

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[sjrl]

This same PR was already closed here #11452 with the reasoning provided here #11452 (comment)