v0.12.1

• Automatic Event Discovery on ARM: Hardware event types are now automatically detected on ARM architectures when initializing a perf::CounterDefinition instance.
• Hardware Counter Introspection: The number of available physical performance counters per logical core, along with the number of events each counter can multiplex, is now determined automatically when creating a perf::EventCounter.
• Recursive and Scientific Metrics: Metric expressions can now reference other metrics recursively. Support for scientific notation (e.g., 1e5) in formula-based metrics has also been added.