Add metaobject instances management API

[mtylty]

This pull request implements comprehensive metaobject instances management functionality, extending the ShopifyToolkit::MetaobjectStatements module with full CRUD operations for metaobject instances.

New functionality for managing Shopify metaobject instances:

• Method create_metaobject: Creates new metaobject instances with validation to ensure the metaobject definition exists. Includes built-in checks to skip creation if an instance with the same handle already exists. (lib/shopify_toolkit/metaobject_statements.rb)

• Method find_metaobject: Retrieves a single metaobject instance by type and handle, returning the complete metaobject data including all fields. (lib/shopify_toolkit/metaobject_statements.rb)

• Method find_metaobjects: Queries multiple metaobjects by type with support for filtering, sorting, and pagination. Supports all Shopify GraphQL query parameters including first, query filters, sortKey, and reverse ordering. (lib/shopify_toolkit/metaobject_statements.rb)

• Method update_metaobject: Updates existing metaobject instances by handle or GID. Gracefully handles cases where the metaobject doesn't exist with user-friendly feedback. (lib/shopify_toolkit/metaobject_statements.rb)

• Method delete_metaobject: Deletes metaobject instances by handle or GID with proper error handling and user feedback for non-existent objects. (lib/shopify_toolkit/metaobject_statements.rb)

Key features:

• Complete CRUD operations for metaobject instances using Shopify's GraphQL Admin API
• Supports both handle and GID-based operations for maximum flexibility
• Proper error handling through the existing handle_shopify_admin_client_errors method
• Gracefully handles edge cases with informative user feedback
• Follows established code patterns and conventions in the module
• Includes the log_time decorator for performance monitoring on write operations
• Full GraphQL query and mutation implementations following Shopify's latest API documentation

Implementation details:

• Uses metaobjectCreate, metaobjectUpdate, and metaobjectDelete mutations
• Leverages metaobject and metaobjects queries for data retrieval
• Maintains consistency with existing metafield and metaobject definition management patterns
• Provides comprehensive field mapping and data transformation
• Updates project README to reflect completed roadmap milestone

Documentation updates:

• README.md: Updated the roadmap to mark "Metaobject Instances management API" as completed, and also marked "Delete" functionality for Metaobject Definitions as completed from the previous PR.

[Copilot]

Pull Request Overview

This PR introduces full CRUD support for Shopify metaobject instances and updates documentation to reflect completed functionality.

• Adds create_metaobject, find_metaobject(s), update_metaobject, and delete_metaobject methods with GraphQL implementations and error handling.
• Updates README checklist to mark metaobject instances management API and delete functionality as completed.
• Leverages log_time for write operations and integrates with existing error handling patterns.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
lib/shopify_toolkit/metaobject_statements.rb	Implements CRUD methods for managing metaobject instances via GraphQL
README.md	Fixes roadmap items to mark delete and instances API as completed

Comments suppressed due to low confidence (1)

README.md:20

• The markdown list items for Delete and Metaobject Instances management API are misaligned; please fix indentation and bullet syntax to ensure these checklist entries render correctly.

  - [x] Delete

[Copilot]

Casting all field values to strings may lead to invalid types for non-string fields; consider preserving original value types or converting based on the metaobject field definitions.

Suggested change

	metaobject_input[:fields] = fields.map { |field| { key: field[:key].to_s, value: field[:value].to_s } } if fields.any?
	metaobject_input[:fields] = fields.map { |field| { key: field[:key].to_s, value: field[:value] } } if fields.any?

[Copilot]

[nitpick] Raising a generic RuntimeError makes it harder to handle this specific error downstream; consider defining and using a more descriptive or custom exception class.

Suggested change

	raise "Metaobject definition #{type} does not exist. Create it first."
	raise MetaobjectDefinitionError, "Metaobject definition #{type} does not exist. Create it first."