Add comprehensive CBOR_Packet unit tests covering nested structures and realistic models

[Copilot]

Expands CBOR test coverage from 378 to 413 passing tests, adding 35 new tests targeting CBOR_Packet with complex field compositions that were previously untested or only minimally covered.

New test categories

• CBORF_PACKET nesting — 3-level deep nesting (ARRAY→ARRAY→ARRAY), CBORF_PACKET inside CBORF_MAP, and the Document/Metadata nested MAP-in-MAP pattern
• CBORF_ARRAY_OF with CBOR_Packet elements — encode/decode/roundtrip/empty, including CBORF_ARRAY_OF embedded in a CBORF_MAP via CBORF_PACKET
• CBORF_optional edge cases — type-mismatch sets field to None, correct type decoded normally, behavior inside CBORF_MAP when key is present vs. absent
• CBORF_SEMANTIC_TAG extended — TEXT_STRING inner (cbor2 decodes to datetime), INTEGER unix timestamp, tag byte major-type assertion, byte-exact comparison with cbor2.CBORTag, inside both CBORF_MAP and CBORF_ARRAY
• Realistic models — EAT-like attestation token, SensorReport with nested CBORF_PACKET inner reading, HttpStatusList (CBORF_ARRAY_OF of CBOR_Packets), HTTP response header map, COSE-like header with negative algorithm value

Notable pitfalls documented via tests

CBORF_INTEGER.val = -7 on a field defaulted to 0 fails at build time because the stored object is CBOR_UNSIGNED_INTEGER; feeding the negative value via cbor2.dumps(...) and dissecting it first is required:

# Wrong: pkt.alg.val = -7  →  CBOR_Codec_Encoding_Error at bytes(pkt)
pkt = CoseHeader(cbor2.dumps({'alg': -7, 'kid': 'key-42'}))  # correct
dec = cbor2.loads(bytes(pkt))
assert dec['alg'] == -7

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[polybassa]

@copilot add more unit test and interoperability tests with the cbor2 library