debugformat: embed raw values in JSON and template output

debugformat: flush formatter output per item

tests: use Python to write binary data in lfs test instead of shell The shell construct here appears to be unevenly supported: it works in /bin/sh on FreeBSD, but it doesn't seem to work when /bin/sh is dash. Using a Python inline directive works fine, so let's just do that instead. Differential Revision: https://phab.mercurial-scm.org/D1636