auth: more RFC3597 conformance

[miodvallat]

Short description

This PR allows records of known type to be provided as raw data, in \# format.

In order to achieve this:

• PacketReader is modified to add a "standalone" mode, in which no header exists before the payload, and no attempt is made to handle compressed DNS names (as compression only works within an entire packet).
• When attempting to parse a known record type from its zone representation, and said representation starts with '#', we parse it as UnknownRecordContent first, then feed the resulting raw data to a PacketReader in standalone mode and then parse the record with the intended type, from the PacketReader.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document, including the AI Policy, and added a "Signed-off-by" to my commits
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Coverage Report for CI Build 29920875492

Coverage increased (+0.05%) to 71.146%

Details

• Coverage increased (+0.05%) from the base build.
• Patch coverage: 18 of 18 lines across 3 files are fully covered (100%).
• 27 coverage regressions across 10 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

27 previously-covered lines in 10 files lost coverage.

File	Lines Losing Coverage	Coverage
pdns/dnsdistdist/dnsdist-tcp.cc	7	74.78%
pdns/axfr-retriever.cc	3	67.47%
pdns/iputils.hh	3	76.26%
pdns/recursordist/pdns_recursor.cc	3	75.69%
pdns/recursordist/recpacketcache.hh	3	91.14%
pdns/tsigverifier.cc	3	77.22%
modules/lmdbbackend/lmdbbackend.cc	2	72.02%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	87.68%
pdns/backends/gsql/gsqlbackend.hh	1	88.57%
pdns/recursordist/syncres.cc	1	81.49%

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Coverage Stats

Relevant Lines:	172039
Covered Lines:	134175
Line Coverage:	77.99%
Relevant Branches:	82302
Covered Branches:	46779
Branch Coverage:	56.84%
Branches in Coverage %:	Yes
Coverage Strength:	8322667.66 hits per line

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💛 - Coveralls

[miodvallat]

Fixes: #804