Use noCache when cache disabled

[lunny]

close #19703
fix #18749

[wxiaoguang]

The no-op cache will make the email-resend-limit lose the protection. If some users disable the cache, they might be exposed to the email spam risk.

#19703 (comment)

[6543]

@wxiaoguang if we do depend on cache already why do we have an option to disable it at all?

[wxiaoguang]

@wxiaoguang if we do depend on cache already why do we have an option to disable it at all?

When I joined this project, the option was already there, and some features have direct dependency on it. That's why I proposed to remove the option to prevent from disabling the cache, and always use a builtin cache (this proposal has been discussed in discord before, see the agreement and the chat history)

In fact, that's how a big project evolves. At the beginning, an option is optional. When new code comes, some optional options changes, they may become required. Such changes, some are caused by well-designed purpose, some are caused by not-well-designed features.

Unfortunately, the email-resend-limit feature was not well designed, to be honest, it didn't take the consideration that the cache could be disabled, then the app panics. Therefore, making email-resend-limit work correctly without cache is also a choice beside always using builtin cache as default.

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Update: indeed, there is a third choice (like these 2 PRs): disable email-resend-limit feature when cache is disabled, as long as most people agree to expose such (small) risk to users who don't know the cache usage details.

(no blocker from my side, I just try to mention the plan and risk which has been discussed before, while always using a builtin cache as default is the best choice in my mind).

[zeripath]

This breaks the unit tests.

[6543]

#19703 can be packported ... this will need more code moving ... - I considder it a refactor