feat(integrations): Add Integration Tasks sub-resource

[vikramlc-cognite]

Summary

Adds TaskHistory/TaskHistoryList/SyncResult data classes and IntegrationTasksAPI (list_history, sync), wired into the IntegrationsAPI aggregator as self.tasks. Builds on the Errors sub-resource from #2828.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that changes existing behavior)
• Refactor (no functional change)
• Documentation update
• Chore / tooling / CI

What changed

• New cognite/client/data_classes/integrations/tasks.py: TaskHistory, TaskHistoryList, SyncResult.
• New cognite/client/_api/integrations/tasks.py: IntegrationTasksAPI.list_history() and .sync() (single-page incremental polling endpoint — caller inspects more_data/next_cursor to continue).
• Wired self.tasks = IntegrationTasksAPI(...) into the IntegrationsAPI constructor, plus testing.py/doc-accessor updates.
• Unit tests in tests/tests_unit/test_api/test_integrations/test_tasks.py and a TestSyncResult data-class test, including explicit-null handling for history/errors.

Why it changed

• Related issue: EDG-827
• Related docs / discussion: wire schema from cognitedata/service-contracts PR #3378; field-level details (warningCount/fatalCount, sources/targets lineage) confirmed against the local odin service implementation.

What to focus on during review

• SyncResult depends on IntegrationErrorList from the Errors sub-resource (the /sync endpoint returns both task history and errors together) — this is why Errors had to land before Tasks in this PR stack, not the other way around.
• list_history() raises ValueError if task_name is given without external_id; sync() raises if neither include_errors nor include_task_updates is set — both have matching Raises: docstring sections and tests.

Test evidence

• pytest tests/tests_unit/ -q → 6,609 passed, 8 failed (pre-existing, unrelated), 6 skipped
• python scripts/sync_client_codegen/main.py verify → sync mirrors up to date
• ruff check / ruff format --check → clean
• mypy → no issues (545 source files)

Risks and unknowns

• sync() is not auto-paginated by design (matches the server's incremental-polling contract) — worth double-checking that's the intended usage pattern rather than an oversight.

Rollout and rollback

• Same beta FeaturePreviewWarning gating as the rest of the module. No migrations. Revert is a straight revert of this commit.

Checklist

• Self-reviewed the diff
• Tests added or updated (or N/A with reason)
• Docs updated (or N/A) — N/A, no public docs page exists yet for this beta API
• No secrets, credentials, or PII committed
• Breaking changes called out above and communicated to affected teams — N/A, no breaking changes