fix(state): vim.validate deprecation warning

[Safenein]

This pull request refactors the validation logic in the add_preset function within lua/reactive/state.lua to fix the deprecation warning (Neovim documentation).

Fixes #26.

[rasulomaroff]

Hi there, thank you for the fix.

What's the minimum neovim version that supports that updated signature?

[Safenein]

Hi, it is deprecated in Neovim 0.11.

Do you need retro-compatibility?

[Safenein]

Here it is.