`Path::from_absolute_path` discards UNC host on Windows, unprefixed `LocalFileSystem` cannot service UNC paths

### **Describe the bug**

On Windows, given a UNC `PathBuf` like `\\server\share\foo`, `object_store::path::Path::from_absolute_path` returns `Path("share/foo")` the host (`server`) is dropped. Combined with `LocalFileSystem` (unprefixed), this means UNC paths cannot be used end-to-end: the host is gone before `LocalFileSystem` could resolve it back to a filesystem path.

I'm filing this for visibility; whether the right fix is in `Path::from_absolute_path`, in `LocalFileSystem`, in documentation ("use `new_with_prefix` for UNC roots"), or somewhere else, I'd defer to maintainer judgement.

### **To Reproduce**

```toml
[dependencies]
url = "2.5"
object_store = "0.13"
```

```rust
fn main() {
let input = r"\\\TestShare\basic_partitioned\";
let canonical = std::fs::canonicalize(input).unwrap();
println!("canonical: {canonical:?}");
let url = url::Url::from_directory_path(&canonical).unwrap();
println!("url: {url}");
let pathbuf = url.to_file_path().unwrap();
println!("to_file_path: {pathbuf:?}");
let store_path = object_store::path::Path::from_absolute_path(&pathbuf).unwrap();
println!("object_store: {store_path}");
}
```

Output (Windows 11, `object_store 0.13.1`, `url 2.5.8`):

```
canonical: "\\\\?\\UNC\\\\TestShare\\basic_partitioned"
url: file:///TestShare/basic_partitioned/
to_file_path: "\\\\\\TestShare\\basic_partitioned\\"
object_store: TestShare/basic_partitioned <-- host dropped
```

Lines 2 and 3 confirm `url` preserves the host across the round-trip. Line 4 is where it disappears.

### **Additional context**

Surfaces as user-visible failures in:

- delta-io/delta-kernel-rs#1482
- delta-io/delta-rs#3551

A `delta-kernel-rs` patch attempting to handle this above the `object_store` boundary did not help, since the host is stripped here regardless of how the caller routes the URL conversion. Documenting this either way (whether as a bug to fix or as expected behaviour with `new_with_prefix` as the prescribed workaround) would unblock those downstream fixes.

### **Potential workaround**

`LocalFileSystem::new_with_prefix(r"\\server\share")` plus share-relative `Path`s appears to work, but requires the caller to know the UNC root in advance — which is awkward for libraries that accept user-supplied URIs.

Start with the Windows reproduction and inspect Path::from_absolute_path, then trace how LocalFileSystem handles UNC paths and its new_with_prefix workaround. Confirm whether the host can be preserved through the existing API; done means either UNC paths work end to end or the supported workaround and its limitations are clearly documented.

Written by the indexing model from the issue text.