debian: T9261: byte-compile the Python library on install

The package ships 188 .py files and zero .pyc. dh_python3 runs and its py3clean
counterpart is present in the generated prerm, but the postinst half is silently
dropped: debhelper only injects autoscripts where its substitution token
appears, and debian/vyos-1x.postinst does not carry one. The package therefore
cleans up bytecode that nothing ever creates.

Call py3compile directly rather than adding the token, which would also inject
the dh_installsystemd enable/start snippets for vyos-router.service and
vyos.target and change service enablement at install time.

vyos/xml_ref/cache.py needs a second pass. It is generated by update_cache.py
from the postinst itself, so it does not exist yet when py3compile walks the
package. It is a multi-megabyte dict literal and by far the most expensive
single file in the tree to parse.

Measured on a fast build host, per interpreter start:

  vyos/xml_ref/cache.py    216.1 -> 32.1 ms  (-85%)
  import vyos.ifconfig      66.8 -> 29.0 ms  (-57%)
  import vyos.config        31.0 -> 20.4 ms  (-34%)

Since dist-packages is writable on an installed image, a root-run script would
eventually populate __pycache__ by itself; this makes it deterministic and
covers live boot, where the overlay is tmpfs and the cost is paid every boot.

0 files changed, 0 insertions, 0 deletions