Enhancement: ignore stale labeling events (#1311)

* Ignore updates if only stale label changed after marking

* Initial tests

* test hasOnlyStaleLabelUpdateSince itself

* Actually we should only ignore label events, not unlabel

* Add logger

* Fix test

* Remove trailing whitespace

* Add test for non-label event

* Add boundary test

* Add error handling to hasOnlyStaleLabelAddedSince

* Add comment noting intentional event before boundary

* Remove unneeded optional chaining

* Limit pagination to max 3 calls / 300 events

* Rename method

* Handle invalid timestamps

* Fallback when limit reached

* Oh wow, just realized we already got events...

* Refactor

* Lint

* Build

* Remove events "cache"

* Update index.js

__tests__/exempt-draft-pr.spec.ts

@@ -129,6 +129,7 @@ class IssuesProcessorBuilder {
       async p => (p === 1 ? this._issues : []),
       async () => [],
       async () => new Date().toDateString(),
+      undefined,
       async (): Promise<IPullRequest> => {
         return Promise.resolve({
           number: 0,