vine: scale task priority multiplicatively

[JinZhou5042]

Proposed Changes

Task priorities can differ by several orders of magnitude, so increasing them by a fixed number internally would be meaningless. Instead, we should scale the priorities multiplicatively to preserve their relative magnitude.

Merge Checklist

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• make test Run local tests prior to pushing.
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[btovar]

I think this is the wrong approach. The objective of the increase in priority is to run the task sooner, and the * 1.05 does not guarantee it. It is easy to set priorities far apart that the issue does not go away. I suggest coming up with a different policy (like having two tasks priorities: user and taskvine and sort first by the taskvine priorities. The priority queue would look at two priorities.)

Because of this, I'm reluctant to merge this one.

[btovar]

I can give the two priorities idea a try tomorrow.

[JinZhou5042]

Handled in #4273