chore: fixup a few review issues

prymer/api/variant_lookup.py

@@ -353,6 +353,20 @@ def __init__(self, vcf_paths: list[Path], min_maf: Optional[float], include_miss
             open_fh = pysam.VariantFile(str(path))
             self._readers.append(open_fh)
 
+    def __enter__(self) -> "FileBasedVariantLookup":
+        """Enter the context manager."""
+        return self
+
+    def __exit__(
+        self,
+        exc_type: Optional[type[BaseException]],
+        exc_value: Optional[BaseException],
+        traceback: Optional[TracebackType],
+    ) -> None:
+        """Exit this context manager while closing the underlying VCF handles."""
+        self.close()
+        return None
+
     def _query(self, refname: str, start: int, end: int) -> list[SimpleVariant]:
         """Queries variants from the VCFs used by this lookup and returns a `SimpleVariant`."""
         simple_variants: list[SimpleVariant] = []
@@ -370,17 +384,6 @@ def close(self) -> None:
         for handle in self._readers:
             handle.close()
 
-    def __exit__(
-        self,
-        exc_type: Optional[type[BaseException]],
-        exc_value: Optional[BaseException],
-        traceback: Optional[TracebackType],
-    ) -> None:
-        """Exit this context manager while closing the underlying VCF handles."""
-        super().__exit__(exc_type, exc_value, traceback)
-        self.close()
-        return None
-
 
 class VariantOverlapDetector(VariantLookup):
     """Implements `VariantLookup` by reading the entire VCF into memory and loading the resulting