v3.2.7 is released

Overview: Gamma supports three storage types: RocksDB, MemoryOnly, and Mmap. v3.2.7 mainly modifies and optimizes Mmap. The specific modifications are as follows:

1. Use a unified way to store vectors and scalars;
2. Use cache to improve query performance;
3. Reduce scalar memory usage;
4. Supports dynamic modification of the cache size, and flexible storage and retraction of memory;
5. Fix the occasional inaccurate query of scalar index