fix: make sub and sid jwt claims optional

The generated session token on the checkout ui extensions doesn't contain:
- The `sid` claim
- The `sub` claim if the customer is not logged in

Making them mandatory causes an `Expected type String, got type NilClass` error

Author: BaggioGiacomo

lib/shopify_api/auth/jwt_payload.rb

@@ -30,12 +30,12 @@ def initialize(token)
         @iss = T.let(payload_hash["iss"], String)
         @dest = T.let(payload_hash["dest"], String)
         @aud = T.let(payload_hash["aud"], String)
-        @sub = T.let(payload_hash["sub"], String)
+        @sub = T.let(payload_hash["sub"], T.nilable(String))
         @exp = T.let(payload_hash["exp"], Integer)
         @nbf = T.let(payload_hash["nbf"], Integer)
         @iat = T.let(payload_hash["iat"], Integer)
         @jti = T.let(payload_hash["jti"], String)
-        @sid = T.let(payload_hash["sid"], String)
+        @sid = T.let(payload_hash["sid"], T.nilable(String))
 
         raise ShopifyAPI::Errors::InvalidJwtTokenError,
           "Session token had invalid API key" unless @aud == Context.api_key
@@ -52,16 +52,6 @@ def shopify_user_id
         @sub.to_i
       end
 
-      # TODO: Remove before releasing v11
-      sig { params(shop: String).returns(T::Boolean) }
-      def validate_shop(shop)
-        Context.logger.warn(
-          "Deprecation notice: ShopifyAPI::Auth::JwtPayload.validate_shop no longer checks the given shop and always " \
-            "returns true. It will be removed in v11.",
-        )
-        true
-      end
-
       alias_method :eql?, :==
       sig { params(other: T.nilable(JwtPayload)).returns(T::Boolean) }
       def ==(other)