preserve float/double distinction in JSON schema output via format metadata

[akkik04]

Directly related to: #9071

Summary

This PR addresses an issue where the JSON schema generator does not distinguish between BASE_TYPE_FLOAT and BASE_TYPE_DOUBLE, emitting both as: "type": "number".This makes the schema less precise for downstream consumers that rely on JSON Schema for: documentation, code generation, and schema introspection

Change

This change updates idl_gen_json_schema.cpp to preserve floating-point precision information using a new "format" key in the metadata.

Testing

• flattests passes locally upon re-building flatc with my new changes
  -verified JSON schema output using flatc --jsonschema shows correct distinction between float and double

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.