Improve Sentinel C++ version

## Issue Description

Type: *enhancement*

### Describe what feature you want

Currently [Sentinel C++](https://github.com/alibaba/sentinel-cpp) contains basic statistic and flow control features. We need to improve it and add more cool features. Some expected features:

- Circuit breaking
- Adaptive system protection
- Parameter flow control (based on LRU and token bucket)
- Token client for cluster flow control
- Integration with Sentinel dashboard

Discussions are welcomed!

Start by reviewing the sentinel-cpp project and its existing statistic and flow-control capabilities. Compare the requested circuit breaking, adaptive protection, parameter flow control, cluster token client, and dashboard integration features, then clarify which feature has an agreed scope. Done requires an explicit decision and implementation criteria for the selected feature.

Written by the indexing model from the issue text.