Add batch support in ZmqProducerStateTable.

[mint570]

The existing batch implementation in ZmqProducerStateTable only calls the individual API repeatedly. This change brings in the real batch implementation:

1. Add a new method in ZmqProducerStateTable, send(), which can batch both SET and DEL operations in a single call.
2. Update the BinarySerializer to encode multiple SET & DEL requests in a single message. The new encoding format is the following:

• db name
• table name
• key1
• number of attrs in key1
• field
• value
• ...
• key2
• number of attrs in key2
• field
• value
• ...

3. Increase ZMQ buffer size from 4MB to 16MB.

[mint570]

@qiluo-msft can you take a look as well? Thanks.

[jarias-lfx]

/easycla

[liuh-80]

@mint570 , there still 7 UT failed, it's blocking this PR, please fix and ping me if you need approve again.

[mint570]

@mint570 , there still 7 UT failed, it's blocking this PR, please fix and ping me if you need approve again.

The failed tests are vs pytest. I am not sure if this PR is causing the failure since the vs pytest doesn't use the new ZMQ API.
I re-triggered the test to run and will see.