feat: imports resource + analytics.get_aggregate_stats (parity B2)

[pbertsch]

Summary

Workstream B2 parity for the AWSYS.CO Python SDK. Implements both the sync and async clients (dual-client SDK).

• New imports resource (client.imports, sync + async) wrapping /api/v1/imports:
  • start(*, provider, access_token, target_namespace=None, scan_only=None) → POST with snake_case body (None optionals omitted)
  • get_status(job_id) → GET /api/v1/imports/{job_id}
  • cancel(job_id) → DELETE /api/v1/imports/{job_id}
  • list(*, limit=None) → GET /api/v1/imports (unwraps {"jobs": [...]})
  • wait_for_completion(job_id, *, poll_interval=2.0, timeout=120.0) → polls until terminal (completed/partial/failed/cancelled), raises TimeoutError on overrun. Sync uses time.sleep; async uses asyncio.sleep.
• analytics.get_aggregate_stats(short_path, *, period=None) (sync + async) → GET /api/v1/links/{short_path}/stats/aggregate. Existing get_stats left untouched.
• Pydantic v2 models: ImportJob, ImportCounts, AggregateStats, DayClicks, HourClicks, DeviceBreakdown, UTMBreakdown, UpgradeForMore (camelCase aliases, matching existing _CamelModel base). Tier-gated breakdowns modeled as Optional.
• imports attached to Client and AsyncClient; new models exported from package surface.
• README sections (Analytics aggregate + Imports + Models table).
• Version bumped 1.2.0 → 1.3.0 (pyproject.toml + awsysco/__version__, kept in sync).

⚠️ Dependency on production

The backing API routes (/api/v1/imports*, /api/v1/links/{id}/stats/aggregate) are currently staging-only — production deploy is pending APPROVE. Therefore:

• This PR is intentionally a DRAFT — do not merge/publish until the routes are live in prod.
• All tests are mocked (MagicMock/AsyncMock); no live HTTP calls are made.

Test plan

• Mocked unit tests pass — imports (start snake_case body + parse, get_status/cancel/list, wait_for_completion pending→completed resolution + TimeoutError) and get_aggregate_stats (free-tier upgrade_for_more + pro-tier device_breakdown), both sync and async
• Full suite green: 177 passed, 26 skipped (skips are pre-existing credential-gated live tests)
• Public surface verified: client.imports / await asyncclient.imports, analytics.get_aggregate_stats, model imports, __version__ == 1.3.0
• Live integration tests — pending prod route deploy (APPROVE)

🤖 Generated with Claude Code

[pbertsch]

Renamed the new Workstream-B2 aggregate-analytics model AggregateStats → AggregateAnalytics for cross-SDK naming consistency with the TS and Go SDKs (which name the equivalent type AggregateAnalytics).

Names only — model fields and logic unchanged. Covers the Pydantic model + __all__/re-export, both sync & async get_aggregate_stats return types and .model_validate calls, the analytics tests, and the README model table. pytest: 177 passed, 26 skipped (credential-gated live tests stay skipped).