refactor: split cli_show_interfaces.go per render mode (#4654)

[psaab]

Summary

Splits the 1396-LOC pkg/cli/cli_show_interfaces.go per render mode plus a
shared RETH/kernel-query helper file. The RETH / physical-member display
logic repeated across the summary/terse/detail/extensive modes and drifted
(the #4328 family of fixes) — collecting the shared helpers in one place
removes the drift surface. Pure code motion, behavior-identical: no logic,
output text, or netlink/sysfs query order changed.

New layout (same package — unexported helpers stay reachable)

File	Declarations	LOC
cli_show_interfaces.go	showInterfaces (dispatch + summary), showInterfacesRethMemberSummary, showTunnelInterfaces	486
cli_show_interfaces_terse.go	showInterfacesTerse	316
cli_show_interfaces_detail.go	showInterfacesDetail, showInterfacesRethDetail (reused by extensive)	265
cli_show_interfaces_extensive.go	showInterfacesExtensive / …Filtered	207
cli_show_interfaces_stats.go	showInterfacesStatistics, showVlans	110
cli_show_interfaces_shared.go	dhcpLease, rethMemberLinkState, rethMemberAttrs, baseIfName	62

Validation

• Byte-identity decl-diff: a go/parser extraction of origin/master's
  single file vs the union of the six new files reports identical=14, bodydiff=0, missing=0, extra=0 — all 14 top-level declarations
  byte-for-byte identical.
• go build ./... clean; go vet ./pkg/cli/... reports only the
  pre-existing cli.go:503 unreachable-code note (untouched file).
• go test ./pkg/cli/... green, including the cli/grpc: show interfaces reth0 / detail / extensive fail for bondless reth — only 'terse' is reth-aware #4328 (RETH) and cli,grpc,remote-cli: text zone/interface views hide per-interface host-inbound overrides + no-stanza default-deny posture + split system-services/protocols #3654
  (host-inbound) output tests that assert the exact rendered text across the
  summary/detail/extensive/member paths — the visible-output byte-identity gate.
• gofmt clean on all six files.
• pkg/cli/README.md gains a "show interfaces render files (refactor: pkg/cli/cli_show_interfaces.go (1396 LOC) — split per-renderer + shared RETH/kernel helpers #4654)"
  section documenting the split.

Closes #4654

🤖 Generated with Claude Code

https://claude.ai/code/session_015oARShYtiJJ2H4UB4nXGqi

[Copilot]

Pull request overview

This PR refactors show interfaces presentation code by splitting the former monolithic pkg/cli/cli_show_interfaces.go into per-render-mode files plus a small shared helper file for RETH/kernel-query helpers, aiming to eliminate renderer drift while keeping behavior and output unchanged.

Changes:

• Split show interfaces into dedicated files for summary/dispatch, terse, detail (incl. shared RETH detail renderer), extensive, and statistics/VLANs.
• Centralize shared helpers (dhcpLease, RETH member link-state / attrs, baseIfName) into cli_show_interfaces_shared.go.
• Document the new layout in pkg/cli/README.md and record the refactor in _Log.md.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/cli/README.md	Documents the new per-renderer file layout for show interfaces and the shared helper surface.
pkg/cli/cli_show_interfaces.go	Retains dispatch + summary renderer and member-summary path; delegates terse/detail/extensive/stats to split files.
pkg/cli/cli_show_interfaces_terse.go	Holds the show interfaces terse tabular renderer.
pkg/cli/cli_show_interfaces_detail.go	Holds show interfaces ... detail renderer and the shared showInterfacesRethDetail block reused by extensive.
pkg/cli/cli_show_interfaces_extensive.go	Holds show interfaces extensive and ... extensive <if> renderer.
pkg/cli/cli_show_interfaces_stats.go	Holds show interfaces statistics and show vlans presenters.
pkg/cli/cli_show_interfaces_shared.go	Shared DHCP + RETH/kernel-query helpers to prevent drift across renderers.
_Log.md	Logs the refactor action and touched files per repo conventions.