Add more compiler warnings and fix a few things they pointed out worth improving/being more explicit about. This adds GCC-12 compatibility out of the box.

Signed-off-by: DL6ER <dl6er@dl6er.de>

.devcontainer/devcontainer.json

@@ -1,11 +1,11 @@
 {
-  "name": "FTL x86_64 Build Env",  
-  "image": "ghcr.io/pi-hole/ftl-build:x86_64-musl", 
+  "name": "FTL x86_64 Build Env",
+  "image": "ghcr.io/pi-hole/ftl-build:x86_64-musl",
   "runArgs": [ "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined" ],
   "extensions": [
     "jetmartin.bats",
     "ms-vscode.cpptools",
     "ms-vscode.cmake-tools",
     "eamodio.gitlens"
-  ],  
-}
+  ]
+}