pmu in use from error to warning

[harp-intel]

Instead of reporting an error an exiting the program, we report a warning to stderr and the log then continue.

[Copilot]

Pull Request Overview

This PR changes the PMU-in-use condition from an immediate error exit to logging a warning and continuing execution.

• Replace fatal PMU busy error and exit with a warning log and status update
• Preserve process flow instead of sending to channelError
• Updated comments to reflect new behavior

Comments suppressed due to low confidence (3)

cmd/metrics/metrics.go:1045

• [nitpick] Rephrase the comment as an imperative statement to match code style, e.g., // Check if PMUs are in use on the target.

// are PMUs being used on target?

cmd/metrics/metrics.go:1057

• Extract the magic register ID "0x30a" into a named constant (e.g., const cpuCyclesRegister = "0x30a") for clarity and easier future updates.

if strings.Contains(line, "Active") && !strings.Contains(line, "0x30a") {

cmd/metrics/metrics.go:1058

• Add a unit or integration test to cover the new PMU-in-use warning path, ensuring the code logs a warning rather than exiting.

slog.Warn("PMU is in use on target", slog.String("target", myTarget.GetName()), slog.String("line", line))