CI png optimized check

.github/workflows/png_file_checks.yml

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+name: png_file_checks
+
+# Check whether all png files are in a valid format
+on:
+  push:
+    paths:
+      - '**.png'
+      - '.github/workflows/**.yml'
+  pull_request:
+    paths:
+      - '**.png'
+      - '.github/workflows/**.yml'
+
+jobs:
+  png_optimized:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install deps
+        run: |
+          sudo apt-get update
+          sudo apt install -y optipng
+
+      - name: Check whether all png files are optimized
+        run: |
+          ./util/ci/check_png_optimized.sh

util/ci/check_png_optimized.sh

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+#!/bin/bash -e
+
+# Only warn if decrease is more than 3%
+optimization_requirement=3
+
+git ls-files "*.png" | sort -u | (
+	optimized=1
+	temp_file=$(mktemp)
+	echo "Optimizing png files:"
+	while read file; do
+		# Does only run a fuzzy check without -o7 -zm1-9 since it would be too slow otherwise
+		decrease=($(optipng -nc -strip all -out "$temp_file" -clobber "$file" |& \
+			sed -n 's/.*(\([0-9]\{1,\}\) bytes\? = \([0-9]\{1,\}\)\.[0-9]\{2\}% decrease).*/\1 \2/p'))
+		if [[ -n "${decrease[*]}" ]]; then
+			if [ "${decrease[1]}" -ge "$optimization_requirement" ]; then
+				echo -en "\033[31m"
+				optimized=0
+			else
+				echo -en "\033[32m"
+			fi
+			echo -e "Decrease: ${decrease[0]}B ${decrease[1]}%\033[0m $file"
+		fi
+	done
+	rm "$temp_file"
+
+	if [ "$optimized" -eq 0 ]; then
+		echo -e "\033[1;31mWarning: Could optimized png file(s) by more than $optimization_requirement%.\033[0m" \
+			"Apply 'optipng -o7 -zm1-9 -nc -strip all -clobber <filename>'"
+		exit 1
+	fi
+)