Changelog: Improvements

refactor: migrate to math/rand/v2

See merge request !2759

Introduce a new `WorkItemsService` to provide high-level API access to GitLab's
work items (epics, issues, and tasks) through GraphQL.

This implementation includes:
- `GetWorkItem(projectPath, iid)`: Get work item by project path and IID
- `GetWorkItemByID(gid)`: Get work item by global ID (string or int64)
- `WorkItem` struct with common fields in idiomatic Go types
- Type conversion utilities for GraphQL responses:
  - `gidGQL`: Parse global IDs (e.g. "gid://gitlab/WorkItem/179785913")
  - `iidGQL`: Convert IID strings to int64
  - `userCoreGQL`: Convert GraphQL UserCore to BasicUser
  - `workItemGQL`: Internal GraphQL response representation with unwrap()
- Comprehensive test coverage including success and error scenarios
- Generated mock interfaces and client registration

This addresses the current gaps in the GitLab Go client:
- No API support for tasks
- Deprecated REST API for epics (replaced by work items)
- High friction for GraphQL usage (manual query construction,
  custom struct definitions, type conversions)

The service follows established patterns in the Go client (service-based
architecture, `RequestOptionFunc` support, `ErrNotFound` for missing resources,
separate internal/public types).

Issue: #2213

Co-authored-by: Timo Furrer <tfurrer@gitlab.com>

Expand `ListWorkItemsOptions` to support most available GraphQL query
parameters for work items, enabling full-featured filtering, sorting,
searching, and pagination capabilities.

Changes:
- Add 30+ filter fields including assignees, labels, milestones,
  iterations, health status, CRM associations, and reactions
- Add time-based filters (created, updated, closed, due dates)
- Add sorting, search, and pagination parameters
- Implement generic `gqlVariables()` function using reflection to extract
  GraphQL variable definitions from struct tags
- Replace manual field mapping with struct tag annotations using format
  `gql:"name Type"`
- Add `variablesGQL` helper type with `Definitions()` and `Arguments()` methods
  for template rendering

The new approach uses reflection to automatically generate GraphQL query
variables from struct fields, eliminating the need to maintain separate field
type mappings. Each field is annotated with its GraphQL name and type via
struct tags (e.g., `gql:"state IssuableState"`).

This refactoring makes it trivial to add new query parameters in the future -
simply add the field to the struct with appropriate tags.

Technical details:
- `gqlVariables()` validates struct tags and only includes non-zero fields
- Template now uses `variablesGQL.Definitions()` for query signature
- Template uses `variablesGQL.Arguments()` for field parameters
- Comprehensive test coverage added for all new fields

This check is _optional_ and only done when the schema file is available at
`schema/gitlab.graphql`.

- Fix doc comment
- Use `range i` syntax
- Use `strings.Cut`

Add full pagination support to `ListWorkItems` by implementing GraphQL
cursor-based pagination following the Relay specification. This allows callers
to efficiently iterate through large result sets.

Changes:
- Add `PageInfo` type to `Response` for GraphQL cursor pagination metadata
- Add `connectionGQL[T]` generic type for unmarshaling paginated responses
- Replace templated queries with static query using nullable variables
- Add `WithNext()` function to handle all pagination styles uniformly
- Update `Scan2()` to use `WithNext()` for automatic pagination
- Return `Response` with pagination info from `ListWorkItems`
- Remove unused `gqlVariable` types and helper functions
- Add comprehensive unit tests for pagination scenarios

`WithNext` previously used inline signaling by returning `nil` when no more
pages were available. This required callers to check for nil, which is easy to
overlook and inconsistent with Go conventions.

Add a second boolean return value following the comma-ok idiom used by map
accesses and type assertions. This makes pagination termination explicit and
harder to miss.

Update `Scan2`, `ExampleWithNext`, and all call sites accordingly.

feat(workitems): Add an initial "Work Items" service with "Get" and "List" methods.

See merge request !2719

## 1.34.0

### 🚀 Features

- feat(workitems): Add an initial "Work Items" service with "Get" and "List" methods. ([!2719](!2719)) by [Florian Forster](https://gitlab.com/fforster)

### 🔄 Other Changes

- refactor: migrate to math/rand/v2 ([!2759](!2759)) by [Ville Skyttä](https://gitlab.com/scop)

# [1.34.0](v1.33.0...v1.34.0) (2026-02-13)

### Bug Fixes

* **workitems:** Use `int64` for global work item IDs. ([f04e3d08](f04e3d08))

### Features

* **request_options:** Add boolean return value to `WithNext`. ([1cd1e1e5](1cd1e1e5))
* **workitems:** Add comprehensive filtering to `ListWorkItemsOptions` ([052a8978](052a8978))
* **workitems:** Add pagination support to `ListWorkItems`. ([cfdf5ee6](cfdf5ee6))
* **workitems:** Add WorkItems service with Get methods ([00925c26](00925c26)), closes [#2213](#2213)
* **workitems:** Implement the `ListWorkItems` method. ([4f8a7092](4f8a7092))