Remove HostMetadata and HostMetadataV6 protobuf messages, consolidate to HostMetadataV4V6

[Copilot]

Description

Consolidates three redundant host metadata protobuf message variants (HostMetadata, HostMetadataV6, HostMetadataV4V6) into a single HostMetadataV4V6 type that carries both IPv4 and IPv6 addresses along with AS number and labels.

Changes:

• Proto: Removed HostMetadataUpdate, HostMetadataRemove, HostMetadataV6Update, HostMetadataV6Remove messages from felixbackend.proto
• Calc layer: Removed separate IPv4/IPv6 callback interfaces (OnHostIPUpdate, OnHostIPRemove, OnHostIPv6Update, OnHostIPv6Remove) and pending state maps from EventSequencer; removed HostIPKey registration from DataplanePassthru
• Dataplane handlers: Updated noencap_mgr, wireguard_mgr, ipip_mgr, bpf_ep_mgr to handle only HostMetadataV4V6Update/HostMetadataV4V6Remove with IP version filtering
• External dataplane: Removed envelope wrapping for deleted message types

Components affected: felix/calc, felix/proto, felix/dataplane

Related issues/PRs

Todos

• [x] Tests
• [ ] Documentation
• [ ] Release note

Release Note

Felix protobuf API consolidates HostMetadataUpdate/HostMetadataV6Update into HostMetadataV4V6Update. External dataplane drivers should update to handle the unified message type.

Reminder for the reviewer

Make sure that this PR has the correct labels and milestone set.

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• release-note-required: This PR has user-facing changes. Most PRs should have this label.
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Other optional labels:

• cherry-pick-candidate: This PR should be cherry-picked to an earlier release. For bug fixes only.
• needs-operator-pr: This PR is related to install and requires a corresponding change to the operator.

Original prompt

Felix protobuf messages includes 3 different HostMetadata variants. HostMetadata, HostMetadataV6, and HostMetadataV4V6. Remove HostMetadata and HostMetadataV6 and use HostMetadataV4V6 instead.

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