improve performance for show vlan brief in large-scale config

[yanjundeng]

What I did

Improve the performance of "show vlan brief" in large-scale testbed

How I did it

Performance issues in "show vlan brief":

1. get_vlan_ports constructs InterfaceAliasConverter(db) per VLAN — that loads the entire PORT table and calls load_db_config() each time. With 800 VLANs that's 800 PORT-table reads.
2. natsorted(list(vlan_ports_data.keys())) runs twice per VLAN (in get_vlan_ports and get_vlan_ports_tagging).
3. get_vlan_ip_address and get_proxy_arp linearly scan all VLAN_INTERFACE keys per VLAN .
4. get_interface_naming_mode() is queried per VLAN.

Fix :
added _get_brief_cache(ctx) that precomputes ip_by_vlan, proxy_arp_by_vlan, ports_by_vlan (natsorted), tagging_by_vlan, naming mode, and the alias converter exactly once per command.

The cache is stashed on the db object (the same pattern the dhcp-relay plugin uses) — safe because click.make_pass_decorator(Db, ensure=True) creates a fresh Db per CLI invocation. InterfaceAliasConverter is only built when SONIC_CLI_IFACE_MODE=alias.

How to verify it

Verify it on Large scale setup.
It reduces the response time from 35s to 5s.

show-vlan-brief-improvement-ut.log

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[mssonicbld]

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[mssonicbld]

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[mssonicbld]

Hi, there are workflow run(s) waiting for approval, you may be first-time contributor. I will notify maintainers to help approve once PR is approved. Thanks!

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[pbrisset]

Good optimization!

[mssonicbld]

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