Extract monitor execution boilerplate into VirtualClientMonitorComponent

[AlexW-F]

Move the iteration/strategy/frequency execution loop from ExecuteCommandMonitor.ExecuteAsync into the base class ExecuteMonitorOnIntervalAsync method. Subclasses now only need to override ExecuteMonitorAsync with their specific monitor logic.

VirtualClientMonitorComponent changes:

• Implement ExecuteMonitorOnIntervalAsync with iteration tracking, MonitorStrategy (Once, OnceAtBeginAndEnd), MonitorIterations, and MonitorFrequency interval support
• Guard nullable property getters (MonitorFrequency, MonitorIterations, MonitorWarmupPeriod) with ContainsKey to return null instead of throwing when the parameter is absent
• Remove conditional in ExecuteAsync so the interval method is always called when the monitor is enabled

ExecuteCommandMonitor changes:

• Change base class from VirtualClientIntervalBasedMonitor to VirtualClientMonitorComponent
• Replace ExecuteAsync override with ExecuteMonitorAsync containing only the command execution logic
• Remove duplicated boilerplate (warmup, iteration loop, strategy handling, error catching)