Use `strict: true` for TS for the SDK package

[infomiho]

[!IMPORTANT] Edit by @sodic, before tackling this, take care of:

• #2010
• #1827

The d.ts file are generated incorrectly if we use inferred function return type to define a type.

If I write a complex function like createAuthUser that does some data transformation, I'd like to use typeof to infer the final return value. Something like this:

type AuthType = ReturnType<typeof createAuthUser>

function createAuthUser() { ... }

Now, let's check the generate d.ts files for this example (the strict one being the expected type):

strict: true

strict: false

You'll notice that the inferred return type is missing some of the type information, for example the identities being optional.