v2.1.2

This is a minor release containing one optimization and some convenience fixes.

• Add early prefix check in blb_rocksdb_query_by_i() to break out of the iterator loop immediately when keys no longer match the seek prefix. This avoids unnecessary iteration and parsing of keys that are lexicographically close but cannot match.
• Fix GCC -Wuse-after-free warning by capturing the old pointer address as uintptr_t before calling realloc(), then logging the integer value instead of the potentially-freed pointer.
• balboa-backend-console: add previously missing -l option to set query result limit as well as add documentation for the query command in usage text.