* refactor: remove the tr_error** idiom
* fix: tr_error::message() is only constexpr in c++20 and up
* chore: silence a couple of g++-12 Wshadow warnings
* test: fuzz test tr_torrent_metainfo.parseBenc()
* fix: better error-checking in benc string parsing
* fix: return benc failure if the parse stack is unbalanced
* fix: stack range error when logging json parse errors
* test: fuzz test tr_variantFromBuf()
* refactor: add SAX-like benc parser
This is the first part of a series of PRs whose end goal is to avoid
the overhead of tr_variant when parsing bencoded data, e.g. when
parsing .torrent files on startup or when parsing announce/scrape
tracker responses.
This PR introduces a SAX-like benc parser, reimplements variant-benc
to use the SAX benc parser (so that we don't have two benc parsers),
and updates the benc + variant tests.
Charles Kerr