Add a new `workitem list` subcommand to the boards command group for querying and displaying work items with extensive filtering capabilities.

The command supports filtering by:
- Status (open, closed, resolved, all)
- Work item types
- Assigned to (including @me alias)
- Severity classification
- Priority
- Area and iteration paths (with subtree support)
- Result limiting

Add  documentation for the new `azdo boards work-item` command and its `list` subcommand. Includes command reference, examples, and integration with the main boards documentation and help reference.

…ation

The standard library's slices.CompactFunc was removed in favor of a custom uniqueByEq function because CompactFunc only removes consecutive matching elements

This change:

- Removes the import of "slices" package
- Implements a manual deduplication algorithm that preserves order
- Maintains the same public API for Unique, UniqueComparable, and UniqueFunc
- Adds comprehensive test coverage for all unique functionality

The new implementation handles empty and nil slices consistently and provides the same functionality without external dependencies.

Extract validation and rendering helpers and simplify state and identity resolution to reduce duplication and unnecessary client creation. Use a map-based approach for requested state categories and append-only helpers for collecting state names. Defer creating Extensions/Identity clients until an identity lookup is required. Use types.Unique for de-duplication and ensure WIQL Top is only set when a positive --limit is provided.

BREAKING CHANGE: default value for --limit changed from 50 to 0 (no
limit). WIQL Top is only applied when --limit > 0.