[Telemetry] Add Rage::Telemetry.every for periodic block scheduling

[Abishekcs]

What this PR does?

• Rage::Telemetry.every now schedules each tick via Fiber.schedule instead of calling the block inline in the root fiber

Why this design?

• Iodine timers fire in the root fiber, which blocks the reactor thread
• Inside a scheduler fiber, the block's I/O hooks into the fiber scheduler and yields to the reactor, keeping the server responsive

[Abishekcs]

@rsamoilov PR is ready for review.

Just a short summary:

I added a block to Rage::Telemetry.every(ms, &block) so that opentelemetry-instrumentation can use this to call the respective block of code they want to run at their respective interval. This block will also serve to calculate the delay in event loop lag.

Also, I wrote a test code which passes locally but kept failing in the CI I have removed it for now

  context "within the reactor" do
      before do
        Fiber.set_scheduler(Rage::FiberScheduler.new)
      end
      after do
        Fiber.set_scheduler(nil)
      end

      it "periodically executes the block" do
        counter = 0
        within_reactor do
          described_class.every(50) { counter += 1 }
          deadline = Process.clock_gettime(Process::CLOCK_MONOTONIC) + 2
          sleep 0.05 while counter < 3 && Process.clock_gettime(Process::CLOCK_MONOTONIC) < deadline
          -> { expect(counter).to be >= 3 }
        end
      end
...

[rsamoilov]

Sorry for the confusion here.

We need to distinguish between Rage::Telemetry.every and event loop lag. every should be a generic method akin to setInterval in JS. It can be use for anything recurring - sampling values, batching and flushing metrics, heartbeats, aggregations, event loop lag. Basically, it should only be wrapping Iodine.run_every, exposing its functionality as a public API.

[Abishekcs]

@rsamoilov made the required changes. please have another look whenever you are free. thank you!

[rsamoilov]

Great start!

There are several comments, but I've approved the PR. Feel free to either continue here or merge it and tackle those in another one.

[Abishekcs]

@rsamoilov made the required changes in this PR itself. Please have another look whenever you are free. Thank you!

[rsamoilov]

Beautiful!