Fix rid state map leak + Refractor .finished

[Qubitium]

1. HIGH IMPACT: @ZhouXingg Fixed a bug/memory leak of rid state map when stream=False. Rid state map cleanup code after yield is not executed since the receiver of the generator early returns and never calls it again. Qubitium@3407263
2. MEDIUM IMPACT: The rest of the changes deal with merging all structures/properties related to req.finished from a simple bool into a BaseFinishReason object.
3. LOW IMPACT: added type hints for some zmq event receivers so ide/coders can actually see real type even if runtime doesn't use them.

Reason for .finished refractor:

• Consolidate the following into a single finished_reason state/property: output_hit_stop_str, hit_stop_str, finish_reason, finished. They are all related to the same Finished state. Having 4 separate vars separate and passing them around makes the code more complex than necessary.
• FinishReason.EOS enum is now a more generic FINISH_MATCHED_TOKEN object which now can handle any future changes where any token/tokens are matched, not just for single EOS. For example, EOT tokens in structured chat models in future code. Some existing chat models already have multiple EOS defined in model/config.json. This allows the FinishReason object to hold the actual token hit instead of fixed enum which would requires another eos_token var in the current structure to know which of the N possible EOS token was hit.

TESTS:

Tests are performed with vllm 0.4.2 since 0.4.3 requires another PR #487 :

• PASS: Matched eos
• PASS: Matched stop_str
• PASS: Length reached
• PASS: dp == 2