feat: support JSON input files for bb verify command

[johnathan79717]

Summary

Adds support for reading JSON-formatted proof, public inputs, and VK files in the bb verify command. This complements the existing --output_format json feature by allowing the JSON files to be consumed for verification.

This enables users who receive JSON proof artifacts from third parties to verify the proof before using it in their circuits (e.g., for recursive verification).

Format Detection

The format is auto-detected by attempting to parse as JSON. If parsing succeeds, the file is treated as JSON; otherwise it falls back to binary format. This is robust and works regardless of file extension.

Usage

# Verify using JSON files
bb verify --scheme ultra_honk -p proof.json -i public_inputs.json -k vk.json

# Works even without .json extension (content-based detection)
bb verify --scheme ultra_honk -p my_proof -i my_inputs -k my_vk

# Mix and match: JSON proof with binary VK
bb verify --scheme ultra_honk -p proof.json -i public_inputs.json -k vk

Test plan

• Build passes
• Tested verify with JSON files
• Tested verify with binary files (no false positive JSON detection)
• Tested verify with mixed JSON and binary files
• acir_tests bb_prove tests pass

[ludamad]

i would expect this field to be 'proof', 'vk' etc not just fields maybe. and that we'd have proper structs that represent the different forms, so this would look more like the rest of our deserialization. Those structs could have a method for reading a json object

[ludamad]

good overall left some comments