feat: add metric sink infrastructure with console sink support and DI…

[medevod]

[1.0.53] - 2026-10-07

Added

• Pluggable Metric Sink Pipeline (IMetricSink):
  • Core IMetricSink abstraction supporting synchronous Emit(IReadOnlyList<IMetricSnapshot>) and asynchronous EmitAsync(...) with bidirectional default interface implementations.
  • In-process snapshot dispatching for centralized logging, file writes, and local persistence.
• Reactive Observable Pattern (ObservableMetricSink):
  • Implementation of IMetricSink and IObservable<IReadOnlyList<IMetricSnapshot>> enabling standard reactive subscriptions (sink.Subscribe(...)) for piping metric snapshots to Rx.NET queries, event channels, or custom log writers.
• Timer-Free Sampling Triggers (MetricSinkTriggerOptions):
  • First-class support for execution-lifecycle triggers evaluated during operation completion (Out / Dispose), completely avoiding mandatory background timers or polling threads:
    • Stride Sampling: Emit snapshots every $N$ executions (EmitEveryNExecutions).
    • Tail / Outlier Sampling: Immediately emit on operation failure (EmitOnFailure) or when duration exceeds latency thresholds (EmitOnSlowDurationThreshold).
    • Probabilistic Sampling: Random percentage sampling (EmitSampleRate).
  • Zero idle CPU and thread overhead; ideal for serverless (AWS Lambda), CLI utilities, and short-lived batch jobs.
• Structured Console Log Sink (ConsoleMetricSink & ConsoleMetricSinkOptions):
  • High-performance console sink formatting metric snapshots into human-readable single-line structured log entries.
  • Configurable ANSI colorization (Colorize), timestamps, custom prefixes, and redirection to any TextWriter for testing.
  • Dedicated formatting for throughput rates, execution counts, and failure rates.
• Fluent Builder & DI Extensions:
  • Registered sinks on MetricFlowOptions: options.AddSink(...), options.AddConsoleSink(...), options.AddObservableSink(...), and options.ConfigureSinkTriggers(...).
  • Fluent builder chaining: builder.AddConsoleSink(...) and builder.AddSink(...).
  • Automatic dependency injection discovery: automatically resolves any registered IMetricSink services from the DI container into metric trackers.
  • Manual and asynchronous flush support: tracker.FlushSinks() and tracker.FlushSinksAsync().
• Roadmap Updates (ROADMAP.md):
  • Updated Section 2 to reflect IMetricSink, ObservableMetricSink, timer-free sampling, and the console sink.
  • Realigned Section 3 to clarify that cloud APMs (AWS CloudWatch, Azure Monitor, Datadog, Prometheus) are natively handled via OpenTelemetry and System.Diagnostics.Metrics.

---