Wire-format and metric overhaul. Both file and UDP ingest now share one
versioned ParseLine that dispatches on the v<N>\t prefix; v1 stays
unchanged, v2 adds $bytes_sent (replacing $body_bytes_sent),
$request_length, $upstream_response_time, and $upstream_status. File
ingest gains the same versioning, and the legacy positional file format
is removed (no live deployments).
Prometheus exposition is rewritten:
- nginx_http_bytes_sent and nginx_http_request_duration_seconds gain
a source_tag label.
- nginx_http_requests_by_source_total gains status_class.
- New v2-only metrics: nginx_http_request_bytes,
nginx_http_upstream_duration_seconds,
nginx_http_upstream_requests_total{status_class}.
- Dropped nginx_http_response_body_bytes_by_source (subsumed by the
dual-labeled bytes_sent metric).
Adds 'make fixstyle' (gofmt -w) and clears all golangci-lint findings
across the repo (errcheck, S1001, ST1005, unused).
Docs in design.md FR-2/FR-8 and user-guide.md are rewritten to present
v2 as the recommended log format.
Pim van Pelt