* replace concurrency worker pools with base models in State.Workers, update code and tests accordingly
* add media attachment caching, slightly tweak default cache config
* further tweak default cache config values
* replace other media attachment db calls to go through cache
* update envparsing test
* fix delete media attachment sql
* fix media sql query
* invalidate cached media entries during status create / update
* fix envparsing test
* fix typo in panic log message...
* add 'updated_at' column during UpdateAttachment
* remove unused func
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Signed-off-by: kim <grufwub@gmail.com>