feat(NODE-5825): add minRoundTripTime to ServerDescription and change roundTripTime to a moving average

[W-A-James]

Description

What is changing?

Monitor changes

• Add rttSamplesMS internal field
• Add roundTripTime getter
• Add latestRTT getter
• add addRttSample method
• Add clearRttSamples method and call in resetMonitorState
• Add RTTSampler class to implement spec-defined minimum and average RTT calculations

RTTPinger changes

• Add monitor field to reference parent Monitor
• Add latestRTT field, initialized to the the monitor's latestRTT value
• Drive by cleanup: refactor measureAndReschedule to use fewer closures and clarify control flow

ServerDescription changes

• Add minRoundTripTime field
• Add roundTripTime field

##### Connection changes
- Add monitor field to connection to facilitate plumbing of minRoundTrip time to connection layer

Is there new documentation needed for these changes?

• No

What is the motivation for this change?

• NODE-5825
• https://github.com/mongodb/specifications/blob/bbb335e60cd7ea1e0f7cd9a9443cb95fc9d3b64d/source/server-discovery-and-monitoring/server-monitoring.rst#rtt-thread

Release Highlight

ServerDescription Round Trip Time (RTT) measurement changes

ServerDescription.roundTripTime is now a moving average

Previously, ServerDescription.roundTripTime was calculated as a weighted average of the most recently observed heartbeat duration and the previous duration. This update changes this behaviour to average ServerDescription.roundTripTime over the last 10 observed heartbeats. This should reduce the likelihood that the selected server changes as a result of momentary spikes in server latency.

Added minRoundTripTime to ServerDescription

A new minRoundTripTime property is now available on the ServerDescription class which gives the minimum rtt over the last 10 heartbeats. Note that this value will be reported as 0 when fewer than 2 samples have been obvserved.

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket