Avoid re-downloading blog feed when rebuilding site in dev

[yurishkuro]

During the build we query Medium to get the list of recent blog posts. In the past it used to only be done when Hugo was starting in dev mode for the first time, but now it seems to happen on every change to the content, which makes editing & viewing the content much more time consuming.

Change detected, rebuilding site (#25).
2025-02-27 10:57:46.409 -0500
WARN  Downloaded RSS feed for: JaegerTracing - Medium
WARN  Post: Jaeger v2 released
WARN  Post: Towards Jaeger v2  Moar OpenTelemetry!
WARN  Post: Making design decisions for ClickHouse as a core storage backend in Jaeger
WARN  Post: Experiment: Migrating OpenTracing-based application in Go to use the OpenTelemetry SDK
WARN  Post: Better alignment with OpenTelemetry by focusing on OTLP
WARN  Post: Introducing native support for OpenTelemetry in Jaeger
WARN  Post: Jaeger Tracing: A Friendly Guide for Beginners
WARN  Post: Adaptive Sampling in Jaeger
WARN  Post: Migrating from Jaeger client to OpenTelemetry SDK
WARN  Post: Jaeger Persistent Storage With Elasticsearch, Cassandra & Kafka

Find a way to avoid repeated fetches of the blog posts once the dev version of Hugo is running (i.e. via make develop)