fix: replace weight calculation with a rounded ceil

[samc]

Looks like we stumbled across a bug in our production middleware that was resulting in some unwarranted internal service errors - looks to us like there's an overflow in the min / max value calculation for random mutually exclusive groups.

I'll use an example from our production code that was giving us trouble to explain the problem.

1. We have a mutually exclusive group (random assignment) with exactly 6 tenants
2. shortlistedCampaigns would then have their weights adjusted to 16 based on the following:

vwo-node-sdk/lib/utils/DecisionUtil.js

Line 1016 in 16df6eb

campaign.weight = Math.floor(100 / shortlistedCampaigns.length);

3) based on that weight, the following would adjust the lower and upper bounds of startVariationAllocation & endVariationAllocation respectively:

vwo-node-sdk/lib/utils/CampaignUtil.js

Line 41 in 16df6eb

const startRange = Math.ceil(variationWeight * 100);

4) this all results in a maximum upper bound of 9600 when it comes time to decide on a variation:

vwo-node-sdk/lib/core/BucketingService.js

Lines 62 to 64 in 16df6eb

	if (bucketValue >= variation.startVariationAllocation && bucketValue <= variation.endVariationAllocation) {
	return variation;
	}

5. which, looking at the algo from _generateBucketValue, looks to default to a max of 10000 based on Constants.MAX_TRAFFIC_PERCENT. This leaves a 4% chance that an assigned bucketed value falls outside the acceptable bounds of all active tests in a group and returns null - failing on this line:

vwo-node-sdk/lib/utils/DecisionUtil.js

Line 1033 in efee33f

campaignKey: winnerCampaign.key

Here's a snapshot of the overflow in action on our production site: