[RFC] Sentinel Rust polyglot version

## Issue Description

Type: *feature request*

### Describe what happened (or what feature you want)

Implement Sentinel in Rust, including basic statistic and flow control functionalities. Some expected features:

- Basic statistic structure (sliding window that can achieve high concurrency and accuracy)
- Rate limiting (based on sliding window, token bucket or leaky bucket algorithm)
- Circuit breaking
- Metrics interface that can pump real-time metrics to outside consumer
- Embedded API server (HTTP-based)

Discussions and contributions are welcomed!

No files, tests, or entry points are named. Begin by turning the requested Rust implementation into a scoped plan and confirm the intended coverage against each listed capability. Done is not defined beyond implementing basic statistics and flow control, circuit breaking, metrics export, and an HTTP API.

Written by the indexing model from the issue text.