fix(provider): validate JSON-compatible objects and values

[halvaradop]

Summary

This pull request improves JSON-compatible value validation through the isJSONObject function.

The function now verifies that the provided value contains only JSON-compatible values, including JSON primitives, arrays, and plain objects. It rejects unsupported values such as functions, symbols, bigints, and non-plain objects such as class instances, Date, and RegExp objects.

Additionally, this PR re-exports the new isPlainObject function, which verifies whether a value is a plain object.

Previously, isJSONObject accepted values such as Date, RegExp, and other objects that inherit from custom prototypes or classes.

Package Structure

The is-json.ts implementation could potentially be moved to the provider-utils package.

The provider package primarily contains provider definitions and types, while provider-utils contains provider-related logic and utility functions. Moving this implementation to provider-utils would keep the package responsibilities more consistent.

Checklist

• All commits are signed (PRs with unsigned commits cannot be merged)
• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)