fix: use incremental hashing in Preset.get_hash() to avoid loading entire file into memory

Preset.get_hash() called f.read() which loads the entire file into
memory before hashing. Use incremental hashlib.sha256().update()
with 64 KiB chunks to prevent unbounded memory allocation on large
or maliciously sized preset files.

Author: Quratulain-bilal

src/specify_cli/presets/__init__.py

@@ -452,8 +452,11 @@ def tags(self) -> List[str]:
 
     def get_hash(self) -> str:
         """Calculate SHA256 hash of manifest file."""
+        h = hashlib.sha256()
         with open(self.path, 'rb') as f:
-            return f"sha256:{hashlib.sha256(f.read()).hexdigest()}"
+            for chunk in iter(lambda: f.read(65536), b''):
+                h.update(chunk)
+        return f"sha256:{h.hexdigest()}"
 
 
 class PresetRegistry: