junos_commit_check: add lab and test for Junos prefix normalization enforcement

[dhalperi]

Add infrastructure to detect and regression-test which Junos configuration
contexts reject unnormalized prefixes (host bits set) at commit time.

Two layers:

• infra/examples/junos-commit-check/: containerlab lab with
  commit_check_rejects and commit_check_accepts check types for empirical
  discovery on vJunos
• snapshots/junos_commit_check/: CI regression test with per-host
  test_parse_warnings driven by validation/parse_warnings.yaml

Empirical results from vJunos 25.4R1.12: Junos rejects host bits in
static route, aggregate route, generate route, OSPF area-range, firewall
from-address, firewall next-ip, and condition if-route-exists. Junos
accepts host bits in prefix-list, route-filter, SNMP client-list, BGP
allow, MPLS LSP install, interface address, and VGA tracking route.

All 7 "rejects" cases are sickbayed pending Batfish implementation
(batfish/batfish#9928 covers static routes only).

Prompt:

Read https://github.com/batfish/batfish/pull/9928. The underlying issue is
the ability to easily detect, automatically, when Junos will reject a
specific piece of syntax. Design a repeatable procedure to do this, and
apply it to this problem.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.50%. Comparing base (21eafe8) to head (c3ae28b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #171   +/-   ##
=======================================
  Coverage   83.50%   83.50%           
=======================================
  Files          87       87           
  Lines        4165     4165           
=======================================
  Hits         3478     3478           
  Misses        687      687           

Flag	Coverage Δ
unittests	83.50% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.