Add MetaDescriptor and Json Schema converter

[m-melgizin]

MetaDescriptor and JSON Schema Conversion

The implementation provides bi-directional conversion between MetaDescriptor and JSON Schema (as JsonObject) formats

Example Usage:

// Create a descriptor
val descriptor = MetaDescriptor {
    node("user") {
        value("name", ValueType.STRING) {
            required()
            description = "User full name"
        }
        value("age", ValueType.NUMBER) {
            default(18)
        }
    }
}

// Convert to JSON Schema
val schema = descriptor.toJsonSchema() 

Resulting JSON Schema representation:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "required": [
    "user"
  ],
  "properties": {
    "user": {
      "title": "user",
      "required": [
        "name"
      ],
      "properties": {
        "name": {
          "title": "name",
          "description": "User full name",
          "type": "string",
          "__indexKey__": "@index",
          "__multiple__": false,
          "__attributes__": {}
        },
        "age": {
          "title": "age",
          "type": "number",
          "default": 18,
          "__indexKey__": "@index",
          "__multiple__": false,
          "__attributes__": {}
        }
      },
      "__indexKey__": "@index",
      "__multiple__": false,
      "__attributes__": {}
    }
  },
  "__indexKey__": "@index",
  "__multiple__": false,
  "__attributes__": {}
}

// Convert back to descriptor
val restoredDescriptor = schema.toMetaDescriptor()

Related Issues:

closes #35
closes #KS-522

[SPC-code]

Please add general MR description and at least one example of usage of schema.

[SPC-code]

Please move it to kscience.commonTest block.

[SPC-code]

Please document all public classes, objects and methods.

[SPC-code]

Better to give different names for forward and backward conversion

[SPC-code]

Does it make sense to make converter private or avoit namespace object at all?

[SPC-code]

This is very strange test design. You can just run function. It will throw an exception if test fails.

[SPC-code]

Aree there any test to actually test conversion correctness?

[m-melgizin]

The current tests already validate:

1. Schema validity - testIsJsonSchemaValid checks that the generated JSON Schema is syntactically correct (via JsonSchema.fromJsonElement from library io.github.optimumcode:json-schema-validator)
2. Round-trip conversion – testIsSerializationAndDeserializationWorksCorrect ensures descriptor → schema → descriptor produces an equivalent structure

If you’d like additional validation of specific schema properties, let me know - I can add targeted test cases.