feat(tests): enhance schema validation error messages with filename context

[ushkinaz]

Adds a helper to the output message to assist in locating "invalid" JSON in in all.json.

Example output:

Error: [File: data/json/items/ammo/shot.json#L94-L109]
 must have required property 'id', but was {
  abstract: 'shotshell_abstract',
  type: 'AMMO',
  name: { str: 'base shotshell', '//~': 'NO_I18N' },
  weight: '47 g',
  volume: '377 ml',
  longest_side: '57 mm',
  flags: [ 'IRREPLACEABLE_CONSUMABLE' ],
  material: [ 'brass', 'plastic', 'lead', 'powder' ],
  symbol: '=',
  color: 'red',
  count: 20,
  stack_size: 20,
  ammo_type: 'shot',
  casing: 'shot_hull',
  __filename: 'data/json/items/ammo/shot.json#L94-L109'
}

[ushkinaz]

It was originally created for my Bright Nights fork, which requires extensive schema changes. Quickly locating problematic entries in all.json is crucial.

Also, a huge thanks for using clear, atomic commits with descriptive messages -- it made backporting ~200 commits so much easier

[ushkinaz]

Arg, I messed up with formatting and cherry-picking, will update soon