Add type restrictions to json

[Vici37]

This is the output of compiling cr-source-typer and running it with the below incantation:

CRYSTAL_PATH="./src" CRYSTAL_HAS_WRAPPER=1 ./typify spec/std_spec.cr
--error-trace --exclude src/crystal/ 
--stats --progress 
--union-size-threshold 2
--ignore-private-defs 
--ignore-protected-defs  
src/json

This is related to #15682 .

[Sija]

Changes to Object.from_json caused a regression, see:

• Failing build: https://github.com/crystal-money/fx-calculator/actions/runs/17417527061/job/49449196413
• Relevant Discord discussion: https://discord.com/channels/591460182777790474/591597160492171264/1412796101551194113