Perform assessments serially to avoid artificially slow snatches (cro…

…ss-seed#571)

Prowlarr pauses multiple requests to a given upstream that are opened in
parallel. While this is convenient for most consumers because it means
they don't have to retry, for cross-seed it's a bit of a different story
because we both search and snatch heavily. In this case, when all the
requests are coming from us, the queueing behavior doesn't really help
us. What we can do is to just move the queueing behavior into
cross-seed, by running assessments in a loop instead of `Promise.all`ing
them, which will make `snatchTimeout` work better.

closes cross-seed#560 

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Improved the efficiency of the candidate assessment process in the
search functionality.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/pipeline.ts

@@ -61,17 +61,27 @@ interface FoundOnOtherSites {
 	matches: number;
 }
 
+async function assessCandidates(
+	candidates: Candidate[],
+	searchee: Searchee,
+	hashesToExclude: string[]
+): Promise<AssessmentWithTracker[]> {
+	const assessments: AssessmentWithTracker[] = [];
+	for (const result of candidates) {
+		const assessment = await assessCandidate(
+			result,
+			searchee,
+			hashesToExclude
+		);
+		assessments.push({ assessment, tracker: result.tracker });
+	}
+	return assessments;
+}
+
 async function findOnOtherSites(
 	searchee: Searchee,
 	hashesToExclude: string[]
 ): Promise<FoundOnOtherSites> {
-	const assessEach = async (
-		result: Candidate
-	): Promise<AssessmentWithTracker> => ({
-		assessment: await assessCandidate(result, searchee, hashesToExclude),
-		tracker: result.tracker,
-	});
-
 	// make sure searchee is in database
 	await db("searchee")
 		.insert({ name: searchee.name })
@@ -94,11 +104,13 @@ async function findOnOtherSites(
 		}))
 	);
 
-	const assessed = await Promise.all<AssessmentWithTracker>(
-		results.map(assessEach)
+	const assessments = await assessCandidates(
+		results,
+		searchee,
+		hashesToExclude
 	);
 
-	const { rateLimited, notRateLimited } = assessed.reduce(
+	const { rateLimited, notRateLimited } = assessments.reduce(
 		(acc, cur, idx) => {
 			const candidate = results[idx];
 			if (cur.assessment.decision === Decision.RATE_LIMITED) {
@@ -113,7 +125,7 @@ async function findOnOtherSites(
 		}
 	);
 
-	const matches = assessed.filter(
+	const matches = assessments.filter(
 		(e) =>
 			e.assessment.decision === Decision.MATCH ||
 			e.assessment.decision === Decision.MATCH_SIZE_ONLY