Rename base64, json, ipset, process, ppbloom, rule, ssurl and cache from
.c to .cpp without touching their contents, and update the CMake source
lists, debian/copyright and the docs.
Ported code keeps -Wall; -Wextra is now opt-in through
ss_strict_warnings() for code written as C++ (the core tests).
check_no_heap.py gains a ratchet baseline for the converted modules,
which still allocate the way the C code did. A new check_cxx_runtime
test verifies with nm that the programs and libshadowsocks-c.a still
need no C++ runtime library, so C consumers are unaffected.
docs/cpp-core.md describes the language profile, the core primitives,
the phase plan and the measured C baseline (77-89 allocations per
connection in ss-server, 27-39 in ss-local). The compatibility contract
now keeps the C11 public header instead of a C11 code base. CLAUDE.md
drops stale libev, submodule and gnu99 references.