getClosedIssues usessince to grab only the needed issues:

const{data:issues}=awaitthis.issues.listIssues({state:'closed',since:releaseRanges[releaseRanges.length-1][1].date});

getMergedPullRequests should do the same instead of paginating over all pull requests in the repo, which can take a while for large projects. If there's nosince param, maybe there's a way to sort by merge time, or we could could potentially uselistIssues as an initial list of all the PR issues that have been updated since the date, and then short-circuit out ofgetMergedPullRequests once it's seen all of them? 🤷‍