- drop the broad `cppcoreguidelines-*` glob: it produced ~4500 findings
(magic numbers, non-private members, owning-memory, pointer arithmetic,
...) that are aspirational and out of scope for the warning gate
- drop modernize-use-equals-default: in this codebase it only yields
false/unsafe positives, e.g. `= default` on a constructor that
explicitly initializes atomic members (which default-init leaves
indeterminate in C++17), and invalid output on constructors with a
member-init list
- drop modernize-pass-by-value: it rewrites constructor parameters to
by-value + std::move, changing public constructor signatures, which is
an ABI-relevant change unsuitable for a library's public headers
- keep the deliberately-listed modernize/readability/performance checks