add support for remote write in tsdb

[agavra]

Summary

This PR adds implementation of the p8s remote write protocol in order to run https://github.com/VictoriaMetrics/prometheus-benchmark against tsdb. In order to avoid requiring protobuf dependencies I flagged it behind a rust config.

Test Plan

Unit tests and manually tested using a python script:

> python3 test_remote_write.py http://localhost:9090
/Users/agavra/Library/Python/3.9/lib/python/site-packages/urllib3/__init__.py:35: NotOpenSSLWarning: urllib3 v2 only supports OpenSSL 1.1.1+, currently the 'ssl' module is compiled with 'LibreSSL 2.8.3'. See: https://github.com/urllib3/urllib3/issues/3020
  warnings.warn(
Testing Remote Write to http://localhost:9090/api/v1/write
Timestamp: 1766091874754ms (2025-12-18 13:04:34)
Protobuf size: 151 bytes
Compressed size: 131 bytes
Response status: 204
Success! Metrics ingested.

Query your data with:
  curl 'http://localhost:9090/api/v1/query?query=test_metric'


> curl 'http://localhost:9090/api/v1/query?query=test_metric' | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   171  100   171    0     0  30180      0 --:--:-- --:--:-- --:--:-- 34200
{
  "status": "success",
  "data": {
    "resultType": "vector",
    "result": [
      {
        "metric": {
          "__name__": "test_metric",
          "env": "test",
          "instance": "localhost:9090"
        },
        "value": [
          1766091874.754,
          "42"
        ]
      }
    ]
  }
}

Checklist

• Tests added/updated
• cargo fmt and cargo clippy pass
• Documentation updated (if applicable)