Factor out duplicate code for writing 4 hex digits #120

Job	Run time
build (C distribution build, -O2 -Wall -W -std=c90 -Wdeclaration-after-statement -Werror)	27s
build (C distribution build (clang), -O2 -Wall -W -std=c90 -Wdeclaration-after-statement -Werror,...	31s
build (C, y, -O2 -Wall -W -std=c99 -Werror)	1m 9s
build (C (clang), y, -O2 -Wall -W -std=c99 -Werror, clang)	35s
build (java, java, javac, -Xlint:all -Werror)	4m 18s
build (go_old, ubuntu-22.04, golang-1.13, go)	30s
build (go_new, ubuntu-24.04, golang-1.22, go)	40s
build (javascript_node, node, nodejs)	5m 19s
build (rust, rust, rustc)	1m 47s
build (csharp, mcs, mono-devel)	4m 14s
build (Pascal, fpc, fpc)	55s
build (Python 3.8, python3.8, ubuntu-20.04, python3.8, 1)	23m 23s
build (Python 3.10, python3.10, ubuntu-22.04, python3.10, 1)	22m 19s
build (Python 3.12, python3.12, ubuntu-24.04, python3.12, 1)	18m 32s
build (Python (pypy3), pypy3, pypy3)	6m 43s
build (Ada, gprbuild, gnat gprbuild)	48s
build (Windows (C), windows-latest, y, sccache)	1m 19s
build (Windows (Go), windows-latest, go, mingw32-make, mingw-w64-ucrt-x86_64-go, sccache)	1m 19s
	1h 34m 48s

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