Open collection-level asset referencing virtual icechunk store (#54)

Using STAC Collection and collection-level assets as described in
https://nasa-impact.github.io/dse-virtual-zarr-workshop/examples/03_STAC_Collection_for_Virtual_Icechunk_Store.html

```python
import pystac
import xarray as xr

collection = pystac.Collection.from_file("https://raw.githubusercontent.com/stac-utils/xpystac/refs/heads/icechunk/tests/data/virtual-icechunk-collection.json")

# Get the latest version of the collection-level asset
assets = collection.get_assets(role="latest-version")
asset = next(iter(assets.values()))

xr.open_dataset(asset)
```

Author: jsignell

README.md

@@ -13,8 +13,9 @@ iterable of items, or output of pystac_client.Client.search.
 | file format | one asset (item or collection-level) | one item | many items | 
 | ----------- | --------- | -------- | ---------- | 
 | COG | x | x | x |
-| zarr | x | | |
-| kerchunk | x | x* | x* |
+| Zarr | x | | |
+| Kerchunk | x | x* | x* |
+| virtual Icechunk | x | | |
 
 \* _if stored in item alongside the datacube extension properties_
 
@@ -43,6 +44,23 @@ asset = item.assets["visual"]
 xr.open_dataset(asset)
 ```
 
+Read from a virtual Icechunk store
+
+```python
+import pystac
+import xarray as xr
+
+collection = pystac.Collection.from_file(
+    "https://raw.githubusercontent.com/stac-utils/xpystac/refs/heads/main/tests/data/virtual-icechunk-collection.json"
+)
+
+# Get the latest version of the collection-level asset
+assets = collection.get_assets(role="latest-version")
+asset = next(iter(assets.values()))
+
+xr.open_dataset(asset)
+```
+
 Here are a few examples from the [Planetary Computer Docs](https://planetarycomputer.microsoft.com/docs/overview/about) which has some good examples of collection-level assets used to catalog zarr stores and
 kerchunk reference files.
 

pyproject.toml

@@ -27,8 +27,10 @@ Repository = "https://github.com/stac-utils/xpystac"
 [dependency-groups]
 dev = [
     "adlfs>=2024.12.0",
-    "aiohttp>=3.11.13",
+    "aiohttp>=3.12.15",
     "fsspec>=2025.3.0",
+    "icechunk>=1.1.5",
+    "ipython>=9.5.0",
     "kerchunk>=0.2.7",
     "odc-stac>=0.3.11",
     "planetary-computer>=1.0.0",

tests/conftest.py

@@ -24,6 +24,12 @@ def data_cube_kerchunk() -> pystac.ItemCollection:
     return pystac.ItemCollection.from_file(path)
 
 
+@pytest.fixture(scope="module")
+def virtual_icechunk() -> pystac.ItemCollection:
+    path = "tests/data/virtual-icechunk-collection.json"
+    return pystac.Collection.from_file(path)
+
+
 @pytest.fixture(scope="module")
 def simple_search() -> pystac_client.ItemSearch:
     client = pystac_client.Client.open(STAC_URLS["EARTH-SEARCH"])