feat(fuzzy): make frecency database path configurable

[soifou]

This adds a new frecency config table with options to enable it, set the database path, and tweak locking.

It also deprecates the old boolean flags fuzzy.use_frecency and fuzzy.use_unsafe_no_lock, showing a heads-up notice when used.

fuzzy = {
  -- OLD
  use_frecency = true,
  use_unsafe_no_lock = false,

  -- NEW
  frecency = {
    enabled = true,
    unsafe_no_lock = false,
  }
}

If an old frecency database directory exists, it will be automatically migrated to the new configurable location, no manual steps needed.

Closes #2006

---

Some side notes:

• The path in state could also be renamed to blink_cmp instead of blink/cmp. The first folder is always empty.
  - Currently, I use utils.notify instead of assert for soft notifications. In v2, I think we can either use assert or completely remove the reference.
• Feel free to rephrase the notification/docs as you see fit.
• While working on the PR, I noticed that the use_unsafe_no_lock setting used here:

  blink.cmp/lua/blink/cmp/fuzzy/init.lua

  Line 23 in 33f0789

  fuzzy.implementation.init_db(vim.fn.stdpath('data') .. '/blink/cmp/fuzzy.db', config.use_unsafe_no_lock)

  is incorrect. It should be config.fuzzy.use_unsafe_no_lock instead. Although, I guess it's not widely used by users.

[Saghen]

Looks great! I think we should use vim.deprecate instead of notifying the user though, that way they can make the change at their leisure without getting a notification on launch.

is incorrect. It should be config.fuzzy.use_unsafe_no_lock instead. Although, I guess it's not widely used by users.

Hah I wonder if a single user has this enabled then. We should still keep it around for crazy lads like #817

[soifou]

A minor issue is that since I removed the fields (to easily detect if the user still has them), it also displays the (non-blocking) message blink.cmp fuzzy → use_frecency Unexpected field in configuration! which runs before fuzzy.validate.

Ideally, we should distinguish a non-existent field from a deprecated field or you see a better way to handle this?

[Saghen]

Thanks! I've dropped the migration as I don't love the idea of doing synchronous IO on startup. The frecency database only stores up to 2 weeks so it shouldn't be a huge deal for users and it's nice to avoid that failure mode. If you feel like making it async is worth the effort though, I'd be open to it.

It looks like vim.deprecate results in a "press Enter" on startup, and only Nvim is special cased to store it in the healthchecks :( Not a huge deal though, I doubt many people have these options set.

The path in state could also be renamed to blink_cmp instead of blink/cmp. The first folder is always empty.

Fyi, the intention is that other blink projects will use the same folder such as blink.pairs or blink.pick