Seal the heap: bounded library heaps and zero-allocation program tests

The programs point libuv, c-ares and Mbed TLS (MBEDTLS_PLATFORM_MEMORY in
the bundled build) at their own FixedHeap before anything runs, mark the
end of startup with heap_seal(), and in verbose mode report heap use and
any allocation after it at exit. The library build keeps the host's
allocator.

measure_alloc.py gains --udp, and the alloc_steady_programs_* tests now
fail on any malloc per relayed TCP connection (by name and by address)
or UDP association, for every cipher family.

src/tunnel.cpp

@@ -58,6 +58,7 @@
 #include "common.h"
 #include "ss_windows.h"
 
+#include "core/heap_guard.hpp"
 #include "relay/tcp.hpp"
 #include "relay/udp.hpp"
 
@@ -246,6 +247,10 @@ plugin_watcher_cb(SS_P_ ss_io *w, int revents)
 int
 main(int argc, char **argv)
 {
+    // Bounded heaps for libuv, c-ares and Mbed TLS before any of them runs.
+    if (!ss::install_library_heaps())
+        FATAL("failed to reserve the library heaps");
+
     int i, c;
     int pid_flags    = 0;
     int mptcp        = 0;
@@ -1051,6 +1056,7 @@ Same behavior as `-V`; see that option for details. Short alias: `-V`.
     }
 #endif
 
+    ss::heap_seal();
     ss_run(loop, 0);
 
     if (plugin != NULL) {
@@ -1071,5 +1077,8 @@ Same behavior as `-V`; see that option for details. Short alias: `-V`.
     winsock_cleanup();
 #endif
 
+    if (verbose)
+        ss::log_heap_report();
+
     return ret_val;
 }