Instance fails to boot after changing instance type (Xen ↔ Nitro) when hibernation is enabled

## Issue Description

When hibernation is enabled on an EC2 instance, amazon-ec2-hibinit-agent sets kernel command line parameters resume and resume_offset. However, the resume parameter is set using device names (e.g.,
resume=/dev/nvme0n1p1, resume=/dev/xvda1). When changing instance types between different hypervisor types (Xen ↔ Nitro), the device naming convention changes, causing the instance to fail boot
with instance status check failures.

## Root Cause

The issue occurs in the patch_grub_config function where the swap device is identified by device name:

https://github.com/aws/amazon-ec2-hibinit-agent/blob/master/agent/hibinit-agent#L131
```python
grub_update_kernel = "grubby --update-kernel=ALL --args='no_console_suspend=1 " + \
"resume_offset={offset} resume={swap_device}'"
grub_update_kernel = grub_update_kernel.format(offset=offset, swap_device=swap_device)
check_call(grub_update_kernel, shell=True)
```

https://github.com/aws/amazon-ec2-hibinit-agent/blob/master/agent/hibinit-agent#L189
```python
if config.grub_update:
dev_str = find_device_for_file(SWAP_FILE)
patch_grub_config(dev_str, offset)
```

https://github.com/aws/amazon-ec2-hibinit-agent/blob/master/agent/hibinit-agent#L210
```python
def find_device_for_file(filename):
# Find the mount point for the swap file ('df -P /swap')
df_out = check_output(['df', '-P', filename]).decode(sys.getfilesystemencoding())
dev_str = df_out.split("\n")[1].split()[0]
return dev_str
```

## Reproduction Steps

1. Launch hibernation-enabled instance with Xen-based instance type:
```bash
aws ec2 run-instances \
--image-id ami-07faa35bbd2230d90 \
--instance-type t2.micro \
--key-name test \
--security-group-ids sg-1234567890abcdef0 \
--hibernation-options Configured=true \
--block-device-mappings '[
{
"DeviceName": "/dev/xvda",
"Ebs": {
"VolumeSize": 30,
"VolumeType": "gp3",
"Encrypted": true
}
}
]'

```

2. Stop the instance:
```bash
aws ec2 stop-instances --instance-ids i-1234567890abcdef0
```

3. Change to Nitro-based instance type:
```bash
aws ec2 modify-instance-attribute --instance-id i-1234567890abcdef0 --instance-type Value=t3.micro
```

4. Start the instance:
```bash
aws ec2 start-instances --instance-ids i-1234567890abcdef0
```

5. Check instance status:
```bash
aws ec2 describe-instance-status --instance-ids i-1234567890abcdef0
```

## Expected Result
Instance should boot successfully after instance type change.

## Actual Result
Instance status check fails with "reachability: failed" status:
```json
{
"Details": [
{
"ImpairedSince": "2025-09-03T02:17:00+00:00",
"Name": "reachability",
"Status": "failed"
}
],
"Status": "impaired"
}
```

## Proposed Solution
Use UUID or filesystem labels instead of device names for the resume parameter to ensure compatibility across different hypervisor types.

Start in agent/hibinit-agent, especially find_device_for_file and patch_grub_config at the referenced lines, and reproduce the Xen-to-Nitro hibernation flow with the listed AWS commands. Trace how the swap device becomes the GRUB resume parameter; done means the instance boots successfully and passes its reachability status check after changing instance types.

Written by the indexing model from the issue text.