test: the PCAP-NG JSON report test is still skipped after #1158 fixed its cause #1795

Describe the bug
tests/integration/test_pcapng_end_to_end.py:177-179 skips PcapngUnescapedKeyTests.test_json_report_of_a_decryption_secrets_block_parses as "blocked on dictdumper". #1152 closed through #1158, which escapes JSON mapping keys inside pcapkit (escape_json_keys and escape_key, pcapkit/dumpkit/common.py:346 and :366). Run without the skip, the test passes, and it is not vacuous: it asserts five frames and the block's name in the report.

Expected behavior
The skip is removed. The class and test docstrings (lines 170-210), which still say the report is unparseable and cite pcapng.py:2244 and common.py:351, are rewritten in the same change.

Additional context
dictdumper 0.8.4.post6 still writes the key raw, so the upstream defect is real but worked around. Found by the #1103 second pass (tests slice) and confirmed by a Sonnet review.