C++20 port 16/16: config parsing on arenas, unit tests in C++ (#3080)

* Rename test_jconf.c to test_jconf_cpp.cpp

* Parse the config file on arenas

read_jconf now reads the file and builds the JSON tree in a scratch arena
that is released before it returns, and copies the parsed strings into one
process-lifetime arena instead of a malloc per string. parse_addr and the
config parser share one address splitter.

Port test_jconf to C++ and cover every field copied out of the parse tree,
a re-read, and the densest file the size limit accepts.

* tests: rename remaining C unit tests to .cpp (no content changes)

* tests: port remaining C unit tests to the C++ test harness

Convert acl, acl_literal, aead2022, base64, buffer, cache (legacy
reference), crypto, ipset, ipset_reference, json, netutils, ppbloom,
process, ref, ssurl and utils tests to test_helpers.hpp. ctest names are
unchanged; every assertion is kept. Build the ported sources with the
strict C++ warning set.

* Run clang-tidy on every ported test

The test regex skipped file names with digits (test_aead2022_cpp.cpp,
test_base64_cpp.cpp); include them, fix the two optional accesses it then
reports, and build test_jconf with the strict warning set.

* docs: per-connection RSS on Linux against the C relay

* test_jconf: check read_jconf results before using them

tests/test_ppbloom_cpp.cpp

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Ping-pong bloom filter (src/ppbloom.cpp): add and membership checks.
+#include <cstdint>
+#include <cstring>
+
+#include "ppbloom.h"
+#include "test_helpers.hpp"
+
+extern "C" {
+int verbose = 0;
+}
+
+namespace {
+
+void test_init_free()
+{
+    SS_CHECK(ppbloom_init(1000, 0.01) == 0);
+    ppbloom_free();
+}
+
+void test_add_check()
+{
+    ppbloom_init(1000, 0.01);
+
+    const char *item1 = "hello";
+    const char *item2 = "world";
+    const char *item3 = "missing";
+
+    // Not in the filter initially.
+    SS_CHECK(ppbloom_check(item1, std::strlen(item1)) == 0);
+    SS_CHECK(ppbloom_check(item2, std::strlen(item2)) == 0);
+
+    ppbloom_add(item1, std::strlen(item1));
+    ppbloom_add(item2, std::strlen(item2));
+
+    SS_CHECK(ppbloom_check(item1, std::strlen(item1)) == 1);
+    SS_CHECK(ppbloom_check(item2, std::strlen(item2)) == 1);
+
+    SS_CHECK(ppbloom_check(item3, std::strlen(item3)) == 0);
+
+    ppbloom_free();
+}
+
+void test_binary_data()
+{
+    ppbloom_init(1000, 0.01);
+
+    const uint8_t data1[] = { 0x00, 0x01, 0x02, 0x03 };
+    const uint8_t data2[] = { 0xFF, 0xFE, 0xFD, 0xFC };
+
+    ppbloom_add(data1, sizeof(data1));
+    SS_CHECK(ppbloom_check(data1, sizeof(data1)) == 1);
+    SS_CHECK(ppbloom_check(data2, sizeof(data2)) == 0);
+
+    ppbloom_free();
+}
+
+} // namespace
+
+int main()
+{
+    SS_RUN(test_init_free);
+    SS_RUN(test_add_check);
+    SS_RUN(test_binary_data);
+    return 0;
+}