Upgrade to Svelte v4

[celldra]

I've upgraded all the packages in the package.json and ran the tests that are in the repository, it has passed all of them.

 ✓ test/localStorageStore.test.ts (15)
   ✓ writable() (1)
     ✓ it works, but raises deprecation warning
   ✓ persisted() (14)
     ✓ uses initial value if nothing in local storage
     ✓ uses existing value if data already in local storage
     ✓ set() (2)
       ✓ replaces old value
       ✓ adds new value
     ✓ update() (2)
       ✓ replaces old value
       ✓ adds new value
     ✓ subscribe() (1)
       ✓ publishes updates
     ✓ handles duplicate stores with the same key
     ✓ handles window.storage event (4)
       ✓ sets storage when key matches
       ✓ sets store to null when value is null
       ✓ doesn't update store when key doesn't match
       ✓ doesn't update store when there are no subscribers
     ✓ allows custom serialize/deserialize functions
     ✓ lets you switch storage type

 Test Files  1 passed (1)
      Tests  15 passed (15)
   Start at  12:23:22
   Duration  704ms (transform 66ms, setup 0ms, collect 54ms, tests 15ms, environment 357ms, prepare 87ms)

Let me know if any extra changes are required, I'm happy to help out.

[joshnuss]

Hi @celldra,

I think this package should still support 3.x as well.
Can you set the package version to ^3.48.0 || ^4.12.0?

Also, if you don't mind, can you prefix the commit message with feat:, that will trigger a new npm version when merged.

[joshnuss]

Or maybe event simpler would be to use a version spec like > 3.48.0

[celldra]

Yeah, that sounds much better. I'm not to familiar with NPM so I apologise about that. I can make the changes now

[joshnuss]

Resolved in #195