Preserve order of entries in expand method

.expand() in all three Expandables was using `set()` to deduplicate
paths following expansion. This was altering the order of the paths,
preventing predicatable expansion

This fix uses `dict.fromkeys` to deduplicate while preserving order

Resolves #346

snakebids/core/datasets.py

@@ -131,7 +131,7 @@ def expand(
             allow_missing=allow_missing
             if isinstance(allow_missing, bool)
             else list(itx.always_iterable(allow_missing)),
-            **{self.entity: list(set(self._data))},
+            **{self.entity: list(dict.fromkeys(self._data))},
             **{
                 wildcard: list(itx.always_iterable(v))
                 for wildcard, v in wildcards.items()
@@ -389,7 +389,8 @@ def sequencify(item: bool | str | Iterable[str]) -> bool | list[str]:
 
         allow_missing_seq = sequencify(allow_missing)
         inner_expand = list(
-            set(
+            # order preserving deduplication
+            dict.fromkeys(
                 sn_expand(
                     list(itx.always_iterable(paths)),
                     zip,

snakebids/tests/test_datasets.py

@@ -335,6 +335,19 @@ def test_expand_deduplicates_paths(self, component: Expandable):
         paths = component.expand(path_tpl)
         assert len(paths) == len(set(paths))
 
+    @given(
+        component=sb_st.expandables(
+            restrict_patterns=True,
+            path_safe=True,
+            unique=True,
+        )
+    )
+    def test_expand_preserves_entry_order(self, component: Expandable):
+        path_tpl = bids(**get_wildcard_dict(component.zip_lists))
+        paths = component.expand(path_tpl)
+        for path, entity_vals in zip(paths, zip(*component.zip_lists.values())):
+            assert bids(**dict(zip(component.zip_lists.keys(), entity_vals))) == path
+
 
 class TestBidsComponentExpand:
     """

typings/bids/layout/utils.pyi

@@ -2,7 +2,7 @@
 This type stub file was generated by pyright.
 """
 
-"""Miscellaneous layout-related utilities."""
+from typing import Sequence
 
 class BIDSMetadata(dict):
     """Metadata dictionary that reports the associated file on lookup failures."""
@@ -66,8 +66,11 @@ class PaddedInt(int):
     def __hash__(self) -> int: ...
 
 def parse_file_entities(
-    filename, entities=..., config=..., include_unmatched=...
-):  # -> dict[Unknown, Unknown]:
+    filename: str,
+    entities: Sequence[str] = ...,
+    config: str = ...,
+    include_unmatched: bool = ...,
+) -> dict[str, str]:
     """Parse the passed filename for entity/value pairs.
 
     Parameters