Some use issue about `WithArgs` in namespace_opts.go

Hello all,

I got some special issue about `WithArgs` in namespace_opts.go. For right now, the code below

```go
func WithArgs(k, v string) NamespaceOpts {
return func(c *Namespace) error {
c.args[k] = v
return nil
}
}
```

Just allow people to use string as value when calling this function. But in the specification, the value may be a slice type. FYI https://www.cni.dev/docs/conventions/#args-in-network-config

I'm not sure if there is some mistake?

Start in namespace_opts.go at WithArgs and compare its string-only value handling with the CNI network configuration args convention linked in the issue. Determine the expected slice-valued behavior and check how NamespaceOpts and c.args are used elsewhere. Done means the API matches the stated convention and relevant behavior is covered by tests.

Written by the indexing model from the issue text.