Fix Issues with BandwidthMeasurementEngine stop method and Performance API

[bekmuradov]

• First, there no stop method in BandwidthMeasurementEngine class. Stop method of this class is called onConnectionError, as shown in the following links::
  https://github.com/cloudflare/speedtest/blob/main/src/engines/BandwidthEngine/ParallelLatency.js#L44
  https://github.com/cloudflare/speedtest/blob/main/src/engines/BandwidthEngine/ParallelLatency.js#L78
  I added stop method which calls this.pause(), which may need to be updated accordingly. See:
  https://github.com/bekmuradov/speedtest/blob/main/src/engines/BandwidthEngine/BandwidthEngine.js#L126-L128
• Secondly. The performance.getEntriesByName() method is returning an empty array, which means there are no timing entries with the specified url. As a result, when attempting to access .slice(-1)[0], it shows warning message and there is no timing data. To fix these issues, we need to ensure that the Performance API is correctly capturing the timing entries for each request.
  • create a performance entry using performance.mark() before making the fetch request and set an identifier for the entry.
  • After receiving the fetch response, create another performance entry using performance.mark() and performance.measure() to calculate the duration of the request.

[vasturiano]

@bekmuradov thanks for making this PR.

The first issue has just been fixed in this PR: #27

As for the second, it is the responsibility of the underlying fetch library to do all the performance marks required for the durations to be calculated correctly. In fact, only that lower level lib would be aware about the different request phases of dns, tcp handshake, request, response, etc.

If you're getting an empty getEntriesByName() it's most likely because the underlying fetch used is not doing these marks correctly, or at all, as is the case with node. Being one of the reasons why this module cannot currently be used in a node-based CLI. More info on this issue: #17 (comment).