feat(operations.pkg): migrate FreeBSD pkg to PackageInfo (phase 2 of #1725)

[wowi42]

Phase 2 of the staged rollout tracked in #1725.

Summary

Migrates the pkg (FreeBSD) manager to the unified package model. Per the rollout direction, the manager exposes a single fact: PkgPackages now returns list[PackageInfo] directly. There are no PkgUpgradeablePackages / PkgLockedPackages sub-facts.

• PkgPackages returns list[PackageInfo] sorted by name, gathered by one compound command: (pkg query '%n %v %k' && echo __pyinfra_pkg_remote__ && (pkg version -vRL= || true)) || pkg_info || true. On FreeBSD, pkg query provides name/version/locked in one pass and pkg version -vRL= (after the marker line) provides available upgrades, so entries carry HELD and UPGRADEABLE statuses. On other BSDs the pkg_info fallback runs and every entry is INSTALLED. The marker presence tells process() which format to parse, so the two formats never mix.
• build_package_map() now returns the same list[PackageInfo] shape (name lives on each entry, so a name-keyed dict only duplicated it). Phase 1 merged after the v3.9.2 release, so this signature change is not in any released version.
• PackageInfo gains to_json() so json_encode can serialize fact output (CLI fact command and the test harness).
• ensure_packages() additionally accepts list[PackageInfo], normalizing to a name-keyed dict internally. Existing dict-shaped callers are unchanged.
• New operations: pkg.update(force=False) (non-idempotent catalog refresh) and pkg.upgrade() (noops when nothing is upgradeable). pkg.packages gains latest; packages locked with pkg lock always noop, even with latest=True.
• Test harness: parse_value in tests/util.py builds PackageInfo from a {"packageinfo": {...}} tagged dict (same spirit as the existing set: / datetime: conventions). Later phases reuse this hook.

Test plan

• New fact fixtures: FreeBSD output with locked, upgradeable, and multi-version packages; pkg_info fallback; empty output.
• New operation fixtures: pkg.update (plain/force), pkg.upgrade (noop/upgrades), pkg.packages with latest (upgrade, up-to-date noop, held noop).
• Existing pkg.packages fixtures updated to the list shape; behaviour unchanged.
• tests/test_facts_packages.py updated for the list return plus a to_json() round-trip test; tests/test_operations_utils.py gains a list[PackageInfo] case.

Requirements

• Pull request is based on the default branch (3.x at this time)
• Pull request includes tests for any new/updated operations/facts
• Pull request includes documentation for any new/updated operations/facts
• Tests pass (see scripts/dev-test.sh)
• Type checking & code style passes (see scripts/dev-lint.sh)

[DonDebonair]

After merging #1878, PackageInfo shouldn't need to_json anymore. JSON encoding is now baked into the test harness.

If you rebase (likely after #1878 merge), I will review so you can continue on the grand plan :)