[ipam/azure] Avoid redundant CiliumNode status writes

[jaredledvina]

On Azure, the operator issued a CiliumNode /status update on essentially every 60s IPAM sync tick for every node, even when nothing changed (~333:1 status:spec write ratio on Azure vs ~2:1 on AWS/ENI). Two things defeated the operator's DeepEqual write-skip gate:

• AzureInterface.DeepEqual compared three json:"-" fields (vmssName, vmID, resourceGroup) that are never serialized to the apiserver, so a freshly rebuilt in-memory interface always differed from the round-tripped origNode copy.
• Status.Azure.Interfaces was built from non-deterministic Go map iteration, so its order changed every call and the index-by-index AzureStatus.DeepEqual saw a change even when the interface set was identical.

Changes:

• Exclude the three non-serialized fields from the generated AzureInterface.DeepEqual (+deepequal-gen=false markers + regeneration).
• Populate Status.Azure.Interfaces in a deterministic, ID-sorted order via a new AzureStatus.SetInterfaces, with the ordering invariant documented on the field.
• Rework Azure native-routing CIDR derivation (deriveVpcCIDRs) to select from the interfaces actually backing the node's IPAM pool allocations (multi-subnet aware), with a pinned-interface preference, a deterministic smallest-ID fallback, and explicit logging of skipped/unparseable CIDRs.

Adds unit tests for the deterministic ordering, the DeepEqual field exclusion (round-trip), and the CIDR selection paths. Azure-only; AWS/ENI is unaffected.

[jaredledvina]

Superseded by #672 and #673. This PR bundled two logically independent changes on disjoint files, so splitting them for clearer review and independent revertability:

• [ipam/azure] Avoid redundant CiliumNode status writes #672 — [ipam/azure] Avoid redundant CiliumNode status writes (the DeepEqual field-exclusion + deterministic SetInterfaces ordering fix; pkg/azure/**).
• [ipam] Derive Azure native-routing CIDR from IPAM pool interfaces #673 — [ipam] Derive Azure native-routing CIDR from IPAM pool interfaces (the deriveVpcCIDRs multi-subnet rework; pkg/ipam/crd.go).

No functional change from this PR — the two branches together reproduce this diff exactly. Closing in favor of #672 and #673.