build: generate hex dump of server assets during build (#6661)

* `build`: generate hex dumps of server assets on the fly

* build: workaround lack of -n on gnu xxd

* build: don't use xxd in cmake

* build: don't call xxd from build.zig

* build: more idiomatic hexing

* build: don't use xxd in Makefile (od hackery instead)

* build: avoid exceeding max cmd line limit in makefile hex dump

* build: hex dump assets at cmake build time (not config time)

examples/server/deps.sh

@@ -8,13 +8,3 @@ PUBLIC=$DIR/public
 echo "download js bundle files"
 curl https://npm.reversehttp.com/@preact/signals-core,@preact/signals,htm/preact,preact,preact/hooks > $PUBLIC/index.js
 echo >> $PUBLIC/index.js # add newline
-
-FILES=$(ls $PUBLIC)
-
-cd $PUBLIC
-for FILE in $FILES; do
-  echo "generate $FILE.hpp"
-
-  # use simple flag for old version of xxd
-  xxd -i $FILE > $DIR/$FILE.hpp
-done