Duplicate session starts on multiple consent updates

[alexanderkirtzel]

Describe the bug
Some CMPs might trigger multiple consent update events for each category/tool. This starts a new session detection process every time. That's making analysis sad.

To Reproduce

On a site with marketing parameters:

elb("walker run");
elb("walker consent", { marketing: true });
elb("walker consent", { marketing: true });

1st event: { event: "session start", data: { count: 1, isStart: true, isNew: true } }
2st event: { event: "session start", data: { count: 2, isStart: true } }

Expected behavior
During a run, the session detection should only run once.