Enhance diagnostics payload with safer shape and raw API context

[MTrab]

Summary

• stop using full device.__dict__ dumps in diagnostics
• keep bug-report value by explicitly including raw API payloads (last_data, settings, dev_data)
• retain useful high-level state fields for quick inspection
• keep redaction for sensitive fields (email, password, lat, lon, acc_email, etc.)
• add diagnostics test coverage for payload shape and redaction behavior

Why

• preserves the original troubleshooting goal (full API response context)
• reduces exposure of private/internal object fields and avoids unnecessary payload bloat

Test strategy

• python3 -m pytest -q tests/test_diagnostics_payload.py tests/test_setup_initial_refresh.py tests/test_options_reload_flow.py
• ruff check custom_components/webastoconnect/diagnostics.py tests/test_diagnostics_payload.py

Known limitations

• payload can still be large when API responses are large; this change is conservative by design

Configuration changes

• none