Mandate `proofs` property to be an array (booth, event proof, event entry proofs)

[filip26]

Require the proofs property for booth, event proof (controller asserted), and event entry proofs (witnessed) to always be an array.

This simplifies proofs processing, c14n, and overall handling, while preventing c14n inconsistencies caused by mixed types and fewer edge cases in multi-proof scenarios.

Union<Map<String,String> | List<Map<String,String>>>
vs
List<Map<String,String>>