Include WAN edge inventory in device lookup

[sashiv20]

Summary

Fix DevicesAPI.get() so callers can resolve WAN edge devices that are present in configuration inventory but absent from the monitored /dataservice/device response on newer vManage trains.

This is the replacement for #197 with the CI-only commits removed, per the maintainer comment on #197 after #198 merged the CI fixes into main.

Root Cause

In the failing vTest run, mtt_aaa.test_create_attach_device_template looked up vm81 with DevicesAPI(provider_session).get().filter(hostname=mt_edge.name).single_or_default(). On vManage 27.1.991-1, /dataservice/device returned only controllers before template attach, so the lookup returned None. TemplatesAPI.attach() then dereferenced device.uuid, producing a raw AttributeError.

Changes

• Preserve the existing monitored-device flow through /dataservice/device and /dataservice/device/system/info.
• Add a best-effort fallback that merges missing WAN edges from configuration device inventory (vedges).
• Broaden DeviceDetailsResponse aliases for newer/older inventory payload field names.
• Raise explicit SDK errors when TemplatesAPI.attach() is called with a missing template or device.
• Add unit tests for inventory-backed device discovery and template attach error handling.

Validation

• uv run pytest catalystwan/tests/test_devices_api.py catalystwan/tests/test_templates.py -> 55 passed, 1 skipped
• uv run flake8 catalystwan/api/basic_api.py catalystwan/api/template_api.py catalystwan/endpoints/configuration_device_inventory.py catalystwan/tests/test_devices_api.py catalystwan/tests/test_templates.py
• uv run mypy --show-error-codes --show-error-context --pretty --install-types --non-interactive catalystwan --cache-dir=.mypy_cache/ --disable-error-code override
• git diff --check origin/main...HEAD

[sbasan]

lgtm