hrTimeToMilliseconds and hrTimeToMicroseconds lose precision

[aabmass]

What happened?

These two util functions are using Math.round() to round to the nearest integer, which causes a huge loss of precision from hrTime:

opentelemetry-js/packages/opentelemetry-core/src/common/time.ts

Lines 131 to 133 in 013695d

	export function hrTimeToMilliseconds(time: api.HrTime): number {
	return Math.round(time[0] * 1e3 + time[1] / 1e6);
	}

opentelemetry-js/packages/opentelemetry-core/src/common/time.ts

Lines 139 to 141 in 013695d

	export function hrTimeToMicroseconds(time: api.HrTime): number {
	return Math.round(time[0] * 1e6 + time[1] / 1e3);
	}

They could instead convert to the correct unit without rounding to an integer.

Steps to Reproduce

const core = require("@opentelemetry/core");

async function main() {
  const start = process.hrtime();
  const end = await new Promise((resolve) => {
    setTimeout(() => resolve(process.hrtime()), 100);
  });
  const dur = core.hrTimeDuration(start, end);
  console.log(dur);
  console.log("Millis diff: %s", core.hrTimeToMilliseconds(dur));
}
main();

Expected Result

Print duration as a floating point milliseconds

[ 0, 100727047 ]
Millis diff: 100.727047

Actual Result

Everything after the decimal is thrown away

[ 0, 100727047 ]
Millis diff: 101

Additional Details

I noticed this while trying out ExponentialHistograms with an HTTP server. I noticed this weird striping in the histograms where any bucket not containing an integer will always have zero count:

because the http instrumentation uses hrTimeToMilliseconds().

OpenTelemetry Setup Code

No response

package.json

No response

Relevant log output

No response

[aabmass]

From SIG: the next step is to make a draft PR fixing this and see if it breaks tests in this repo or contrib.