refactor: Add mem module to allow tests to override allocators.

This will allow us to do more interesting things with memory allocation
within toxcore, and allow fuzzers to explore various allocation failure
paths.

.github/scripts/coverage-linux

@@ -9,7 +9,7 @@ sudo apt-get install -y --no-install-recommends \
   libopus-dev \
   libsodium-dev \
   libvpx-dev \
-  llvm-11 \
+  llvm-14 \
   ninja-build
 git clone --depth=1 https://github.com/ralight/mallocfail /tmp/mallocfail
 cd /tmp/mallocfail # pushd
@@ -21,7 +21,7 @@ export CC=clang
 export CXX=clang++
 
 sudo install other/docker/coverage/run_mallocfail /usr/local/bin/run_mallocfail
-(cd other/proxy && go build)
+(cd other/proxy && go get && go build)
 other/proxy/proxy &
 
 . ".github/scripts/flags-coverage.sh"
@@ -58,4 +58,4 @@ cd - # popd
 #  --exclude testing \
 #  --gcov-options '\-lp'
 
-bash <(curl -s https://codecov.io/bash) -x "llvm-cov-11 gcov"
+bash <(curl -s https://codecov.io/bash) -x "llvm-cov-14 gcov"