[PATCH proxmox,widget-toolkit 0/2] fix #8227: support encapsulated bond hash policies

[i@leaskh.com]

Hi,

This series fixes PBS bug #8227:
https://bugzilla.proxmox.com/show_bug.cgi?id=8227

An operational Linux 802.3ad bond using encap3+4 makes PBS reject
/etc/network/interfaces and prevents the Network Interfaces list from
loading. Linux and ifupdown2 support the policy; the shared Rust API's
enum and the shared UI selector currently list only the three layer*
policies.

Patch 1/2 targets proxmox.git and adds encap2+3 and encap3+4 to the enum,
generated schema and Display implementation. It includes validation and
configuration round-trip regression tests. Existing values and invalid
name validation are preserved.

Patch 2/2 targets proxmox-widget-toolkit.git and exposes the two policies
in the shared selector. It is the companion UI change to patch 1/2.

Validation:
- Native Linux x86_64: all 30 network API library tests pass with the
  impl feature. Against the old enum, the two new acceptance/round-trip
  tests fail with the expected policy rejection.
- Round trips cover five policies, both 802.3ad/balance-xor modes and
  both keyword spellings, including an unrelated following bridge.
- JavaScript syntax and selector-definition runtime checks pass.
- Rust formatting, whitespace and patch application checks pass.

The Linux build used a disposable workspace restricted to ten local
crates, including the network API, omitting non-target dev resolution.
The build setup did not alter library sources. Dependencies came from
crates.io and OpenSSL headers were unpacked privately. This is not a
full Debian package build or an end-to-end GUI test, and no running
host's network configuration was changed.

I emailed my Individual CLA privately to office@proxmox.com today,
identifying Leask Wong <i@leaskh.com> as my Git author identity.
CLA registration has not yet been verified.

The existing Bugzilla attachments contain the same code changes:
https://bugzilla.proxmox.com/attachment.cgi?id=2193
https://bugzilla.proxmox.com/attachment.cgi?id=2194
These mail patches additionally include the requested sign-off trailer.

Please review, and let me know if any changes are needed.

Thanks,
Leask