chore: timeout parameter for notifications shouldn't be required

[mcmxcdev]

• update timeout paramter in interface TNotifier to be optional

Closes https://github.com/beyonk-adventures/svelte-notifications/issues/29

Note that the project could benefit from https://editorconfig.org/ or prettier config to set code style. I had to change my local prettier settings to conform to the project style. The changed index.d.ts file didn't conform to the project style, so there are a couple of formatting changes too.