Check for user namespaces in FUSE filesystems with `allow_other`

### Description

The file access check for FUSE filesystems mounted with the `allow_other` mount option should take user namespaces into account.

### Steps to reproduce

_No response_

### runsc version

```shell

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### docker version (if using docker)

```shell

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### uname

_No response_

### kubectl (if using Kubernetes)

```shell

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### repo state (if built from source)

_No response_

### runsc debug logs (if available)

```shell

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