feat: add CoreExternalDevice API coverage

[jmcte]

Summary

• add CoreExternalDevice wrapper coverage for Bluetooth, permissions, printer, and external storage APIs
• register the module in package exports and docs status
• add focused unit tests for request construction and namespace coverage

Tests

• python -m pytest tests/test_core_external_device.py

[joeperpetua]

Are all these unit tests useful at all? What do they actually test? Just that the request fires? If no actual logic is being tested, then I don't see the purpose for there even being tests.

[N4S4]

I agree with @joeperpetua

[jmcte]

Thanks, that was fair feedback. I updated the tests so they now assert request contracts instead of only checking that request_data was called. They validate the API namespace, path, version, DSM method, request parameters, optional parameter omission, and boolean conversion for representative wrapper methods. I made the same adjustment on the CoreNetwork PR because it had the same test pattern.