[Minor] Backport ucl_object_iterate_end() from libucl to fix iterator leak

[Minor] Backport ucl_object_iterate_end() from libucl to fix iterator leak

Add ucl_object_iterate_end() function to free resources associated with
an inline iterator when iteration is abandoned before completion. This
fixes a potential memory leak when iterating over UCL_OBJECT types where
internal heap state is allocated.

Changes backported from libucl 0.9.3:
- Add ucl_hash_iterate_free() to ucl_hash.c/h
- Add ucl_object_iterate_end() to ucl_util.c and ucl.h
- Add ucl_iterate_object_end macro alias

Note: Rspamd already had the security fixes for:
- heap-buffer-overflow in ucl_maybe_parse_number
- heap-buffer-overflow in ucl_parse_multiline_string
- Use-After-Free in ucl_hash_insert
- Invalid JSON emission when merging objects