Align Tokenizer in JetStream

[JoeZijunZhou]

• Return token ids instead of custom decode operation result in JetStream; let client do tokenizer decode operation
• Update benchmark script and requester tool to use JetStream tokenizer seqio library for tokenizer decode operation
  • Use correct method to let tokenizer decode the whole output token id list
• Update unit tests for the above change
• Enforce python type check to benchmark script
• Update README unit test section