Schema: add effectful constructors to Struct and Class to allow effectful defaults

[adrian-gierakowski]

What is the problem this feature would solve?

I'd like to be able to add defaults for properties of type Date\DateTime, which would default to current time if not set.

Currently the default cannot be created via the Clock service (like with DateTime.now) since defaults cannot be effectful.

What is the feature you are proposing to solve the problem?

Add static makeEffect (effectful counterpart of make) to Struct and Class and and allow effects to be used in constructor defaults and in optionalWith

What alternatives have you considered?

currently it's possible to achieve effectul defaults when encoding and decoding by creating a custom transform. This has a couple of drawbacks:

1. one needs to actually encode\decode to generate the default
2. the property cannot be made required on both sides of the transform (for encoding defaults, decoded prop needs to be optional, and vice versa)

implementation of effectful encode\decode defaults can be found here (decode) and here (encode)

related issue: #3919
related discrod thread: https://discord.com/channels/795981131316985866/1304719283263246400