Nominatim: cache responses

The usage policy asks to "enable caching of requests" and warns that repeating
identical queries may result in blocking, but every submit hit the network --
searching the same term twice sent two identical requests.

Reuse the response of an identical earlier request, keyed by URL and
parameters. The promise is cached rather than the result, so concurrent
identical requests share one fetch, and a cache hit neither waits for a rate
limit slot nor consumes one. Failed requests are evicted so they can be retried.

https://operations.osmfoundation.org/policies/nominatim/