fix: fix pagination cursor handling in beta.skills.list

[xodn348]

Fixes #1391.

This updates beta.skills.list() to use the cursor parameters returned by the standard page type:

• switch list pagination from page to after_id / before_id
• return SyncPage / AsyncPage instead of cursor-page types
• update generated resource tests for the corrected parameters and page types

I rebased this on current upstream/main and kept the patch limited to the Skills list pagination surface.

Testing:

./scripts/test tests/api_resources/beta/test_skills.py -q -n0

Result: 90 passed for Python >=3.9 / Pydantic v2, 90 passed for Python >=3.9 / Pydantic v1, and 90 passed for Python >=3.14 / Pydantic v2.

[localden]

Thank you for the PR - src/anthropic/resources/beta/skills/skills.py, src/anthropic/types/beta/skill_list_params.py are auto-generated from the OpenAPI spec via Stainless, so manual edits here will be overwritten on the next codegen run. If this is a spec issue, it needs to be fixed upstream. Closing.