Fix the problem that CodeFactory is null when specifying snappy format when java Client compresses data

When flink-avro writes data in batches based on the avro format, the general user will specify snappy compression. However, in the avro-1.10.0 version, the Codec and CodeFactory are returned by directly applying for the object, so that the user cannot obtain it Information for SnappyCodec.
I refer to the practice of ```NullCodec```, changing it to a global variable way will work fine

Before repair:

after Repair: