Add default None values to Optional fields

[lmagyar]

Proposed Changes

In mashumaro we have to add default values to fields that can be missing (see https://github.com/Fatal1ty/mashumaro/issues/283#issuecomment-2832041685)

As I see there were issues in the past, when TS removed fields, without notice, and that broke this API immediately. This PR will fill the missing optionals fields with None.

Note: #1265 also needed.

Related Issues

fixes #1262 closes #1263

[lmagyar]

I've tested this PR and #1265 in real life, they are working.