fix!: Ensure that nested structs will deeply serialize

[tbconroy]

The HashSerializer would fail to serialize structs nested more than one level deep even if option should_serialize_values was set to true.

For example, if we update the Job test objects to have a Money Struct for salary, i.e.:

Job.new(title: "Software Developer", salary: Money.new(cents: 90_000_00))

Then, we serialize the Person:

serializer = Typed::HashSerializer.new(schema: Typed::Schema.from_struct(Person), should_serialize_values: true)

serializer.serialize(ALEX_PERSON)
# => {name: "Alex", age: 31, stone_rank: "pretty", job: {title: "Software Developer", salary:<Money cents=9000000 currency=#<Currency::USD>>, needs_credential: false}}, result)

It should probably be:

serializer.serialize(ALEX_PERSON)
# => {name: "Alex", age: 31, stone_rank: "pretty", job: {title: "Software Developer", salary: {cents: 9000000, currency: "USD", needs_credential: false}}, result)

The main change is adding a nested_hash serializer type to lib/sorbet-schema/t/struct.rb. This will deep serialize structs to when hashes.

This new type is used in lib/sorbet-schema/serialize_value.rb so that values of values are recursively serialized.

[maxveldink]

Just need to remove the version bump change and we should be good to go!