Add normal-admin radio diagnostic reads

[MarcLeinenDE]

Adds two read-only radio-diagnostic helpers that reflect the upstream normal-admin transport constraint.

Scope:

• client.mobile.carrier_aggregation_info() → cm/get_ca_info
• client.mobile.radio_metrics() → cm/query_eng_info
• both dispatch as one-member /api.cgi?multicalls=1 requests
• no member data body is sent
• raw inner response objects are preserved; no CA/radio field schema is invented
• malformed multicall envelopes raise ProtocolError

Upstream evidence:

• both methods are LIVE_VERIFIED_LIMITED, ADMIN_MULTICALL_ONLY, READ_OR_LOW_SIDE_EFFECT
• normal-admin direct path/method dispatch is authorization-denied
• a one-member multicall is sufficient

Physical ACIY.3 evidence (2026-09-08):

• targeted test_mobile_status_reads passed 1/1 in 0.77 s on Python 3.13.5
• both helpers succeeded through one-member multicalls
• successful physical execution confirms the expected single-object responses envelope
• no cell IDs, bands or radio measurements were printed; no write/connectivity transition occurred

Safety/privacy:

• no engineering-mode/band write
• get_ca_info emptiness is not interpreted as absence of 5G
• query_eng_info raw/missing metrics are not synthesized or normalized

Documentation:

• CHANGELOG records helper and physical validation
• docs/radio-diagnostics-read.md records transport constraints, semantics, privacy and evidence
• no nr2301-api change is required because the multicall-only authorization behavior and one-member sufficiency were already documented upstream

Validation:

• initial PR CI run #239: Python 3.10/3.11/3.12/3.13 and package all SUCCESS
• final PR diff reviewed; only intended SDK/test/documentation changes remain