Add unchecked DFS tree return method to support DFS referral queries via IPC$ shares

[davelil4]

Problem

When querying DFS referrals via an IPC$ share (common pattern for resolving domain-based DFS namespaces), as_dfs_tree() in fails with "Tree is not a DFS tree" because technically IPC shares do not have the proper flags set (dfs_root or dfs).
This is a standard approach used by other smb libraries (like pythons smbprotocol which tries to connect to \\server\IPC$ and send FSCTL_DFS_GET_REFERRALS to resolve DFS paths. The server accepts these requests on IPC$ even though the share is not a DFS root.

Solution

Add as_dfs_tree_unchecked() method to Tree that just returns a DfsRootTreeRef without actually verifying the share flags:

pub fn as_dfs_tree_unchecked(&self) -> DfsRootTreeRef<'_> {
   DfsRootTreeRef::new(self);
}

Use Case

Resolving domain-based DFS paths like \\domain.com\share\path:

1. Direct connect connection to \\domain.com\share fails (not a server)
2. Connect to IPC$ on a domain controller IP
3. Query DFS referrals via `dfs_get_referrals(r"\domain.com\share")
4. Connect to the resolved target

Without as_dfs_tree_unchecked() this fails because of the check for the DFS flags.

Alternatives

1. Modifying the IPC share flags which is not a good idea
2. Deeper api changes