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)

.gitignore

@@ -34,6 +34,7 @@ lcov-report/
 gcovr-report/
 
 build*
+!build.zig
 cmake-build-*
 out/
 tmp/
@@ -100,6 +101,9 @@ qnt-*.txt
 perf-*.txt
 
 examples/jeopardy/results.txt
+examples/server/*.html.hpp
+examples/server/*.js.hpp
+examples/server/*.mjs.hpp
 
 poetry.lock
 poetry.toml