chore: add .gitattributes to preserve line endings in HTTP fixtures

Treat HTTP fixture files as binary to prevent Git from converting their
line endings. This ensures the Content-Length headers remain accurate
and the fixtures maintain their original format during sync operations.

Author: weppos

.gitattributes

@@ -0,0 +1,4 @@
+# Preserve line endings in HTTP fixture files
+# These files contain raw HTTP requests/responses. Treat them as binary
+# to prevent Git from converting line endings.
+fixtures/**/*.http binary