[performance] processing media and scheduled jobs improvements

[NyaaaWhatsUpDoc]

Changes:

• use runners.Processor{} to ensure singular running instance of processing media/emoji
• retry processing media / emoji if error is due to context cancel during request callstacks
• use simply runners.WorkerPool{} instead of wrapping concurrency package for simplicity
• start moving some workers to state object
• emoji are only ever processed synchronously, remove separate emoji worker pool (also scales up media worker pool to accomodate)
• use runners.Scheduler{} instead of cron, and add to state workers for management
• testrig is now only included in binary if DEBUG=1 is set during build

Checklist:

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.

[NyaaaWhatsUpDoc]

Okay I'll try get to that singular test failure tomorrow 🤔

[tsmethurst]

looks good to me! good work :) the retry of processing on canceled contexts is gonna be really handy i think

[tsmethurst]

license