fix(cdmq): off-by-one duration calculation for partial boundary documents in calcAvg

[atheurer]

Problem Description

In cdmq/cdm.js, metric queries divide the time domain into resolution windows with inclusive millisecond timestamps:

• timeWindowDuration = thisEnd - thisBegin + 1 (cdm.js:3517)
• Stored metric_data.duration is generated as end - begin + 1 (rickshaw-gen-docs:501)
• Query denominator is totalWeightTimesMetrics = timeWindowDuration * numMetricIds (cdm.js:3518)

However, when trimming partial documents that straddle window boundaries in calcAvg(), docDuration is calculated using end - begin without + 1:

https://github.com/perftool-incubator/CommonDataModel/blob/main/queries/cdmq/cdm.js#L3593-L3604

Object.keys(partialDocs).forEach((id) => {
  var docDuration = partialDocs[id].end - partialDocs[id].begin;
  if (partialDocs[id].begin < thisBegin) {
    docDuration -= thisBegin - partialDocs[id].begin;
  }
  if (partialDocs[id].end > thisEnd) {
    docDuration -= partialDocs[id].end - thisEnd;
  }
  var valueTimesWeight = partialDocs[id].value * docDuration;
  sumValueTimesWeight += valueTimesWeight;
  sumWeight += docDuration;
});

Because + 1 is omitted, each boundary document contributes 1 ms less duration than it actually spans inside the window. For example:

• A document spanning [900, 1100] inside window [1000, 2000] has an inclusive overlap of [1000, 1100] (101 ms).
• The current calculation produces (1100 - 900) - (1000 - 900) = 200 - 100 = 100 ms.

Proposed Solution

Simplify the boundary overlap calculation to directly compute the clamped inclusive interval:

Object.keys(partialDocs).forEach((id) => {
  var overlapBegin = Math.max(partialDocs[id].begin, thisBegin);
  var overlapEnd = Math.min(partialDocs[id].end, thisEnd);
  var docDuration = overlapEnd - overlapBegin + 1;

  var valueTimesWeight = partialDocs[id].value * docDuration;
  sumValueTimesWeight += valueTimesWeight;
  sumWeight += docDuration;
});