Recording metrics in-process using MeterListener

A deep dive into using `MeterListener` from the `System.Diagnostics.Metrics` APIs to consume and aggregate metrics in-process within a .NET application. The post walks through building a `MetricManager` wrapper class that subscribes to specific ASP.NET Core and .NET runtime instruments, handles both standard and observable instrument types, and aggregates measurements using thread-safe primitives like `Interlocked`. A live-updating console table powered by Spectre.Console displays the collected metrics. Key concepts covered include selecting which instruments to listen to, triggering observable instruments via `RecordObservableInstruments()`, handling different measurement types with typed callbacks, and the performance rationale behind the API design.