that the scanner was run, the ttlcache was also created each time.
This caused (under testing with 166 genres in the database) the
memory consumed by navidrome to 101.18MB over approx 3 days; 96%
of which is in instances of this cache. Swapping to a singleton
has reduced this to down to ~ 2.6MB
Co-authored-by: Rob Emery <git@mintsoft.net>
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