API limit restrict output to user, but doesn't restrict amount of data from mongodb

If we do two queries:
curl "https://staging.kernelci.org:9000/latest/nodes?kind=test&limit=1"
real 0m5.994s
user 0m0.012s
sys 0m0.000s

curl "https://staging.kernelci.org:9000/latest/nodes?kind=checkout&limit=1"
real 0m0.023s
user 0m0.012s
sys 0m0.000s

We can notice significant difference in response time. While it should be fast both (kind is indexed).

On preliminary investigation reason is that search query submitted to mongodb without limit parameter, which is causing very large output in case of some queries.
We need to resolve that, as it is also causing excessive load on database and ram consumption.

Start by tracing the /latest/nodes endpoint and its MongoDB query, using the two curl examples to compare kind=test and kind=checkout with limit=1. Confirm that the requested limit reaches the database query, then verify response timing and database resource use for both cases.

索引モデルが issue の本文から書いたものです。