[feature/chore] Add Move database functions + cache

[tsmethurst]

Description

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This pull request adds database functions, cache, and helpers for storing and retrieving account Move activities (or indeed any kind of Move activity).

Will be needed for the upcoming Move PR; PR'd separately here to avoid that one becoming massive.

Part of #130

Checklist

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• 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 not leveraged AI to create the proposed changes.
• 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]

one or two questions but otherwise looking good :) as discussed in matrix will be saving squerge of this (once questions resolved) util after v0.14.0 final release 👍