fix: shared-sub with nl sub-option should cause protocol error

[JimMoen]

Fixes EMQX-10238
CI needs emqx/paho.mqtt.testing#13 merged.

Summary

🤖 Generated by Copilot at 178711f

Fix protocol error for shared subscriptions with no local flag in MQTT v5. Improve reason code handling and add test case for emqx_packet module.

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/{ce,ee}/(feat|perf|fix)-<PR-id>.en.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• [~] Schema changes are backward compatible

Checklist for CI (.github/workflows) changes

• If changed package build workflow, pass this action (manual trigger)
• [~] Change log has been added to changes/ dir for user-facing artifacts update

[coveralls]

Pull Request Test Coverage Report for Build 5294902548

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 45 unchanged lines in 13 files lost coverage.
• Overall coverage decreased (-0.02%) to 81.754%

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Files with Coverage Reduction	New Missed Lines	%
apps/emqx_dashboard/src/emqx_dashboard_middleware.erl	1	66.67%
apps/emqx_ft/src/emqx_ft_storage_exporter_fs.erl	1	80.43%
apps/emqx_gateway_exproto/src/emqx_exproto_gcli.erl	1	64.15%
apps/emqx_modules/src/emqx_modules_schema.erl	1	96.3%
apps/emqx/src/emqx_banned.erl	1	92.54%
apps/emqx/src/emqx_broker.erl	1	88.76%
apps/emqx/src/emqx_message.erl	1	94.83%
apps/emqx/src/emqx_ws_connection.erl	1	76.37%
apps/emqx_resource/src/emqx_resource_buffer_worker.erl	3	93.39%
apps/emqx/src/emqx_channel.erl	3	87.71%

Totals
Change from base Build 5280102708:	-0.02%
Covered Lines:	29860
Relevant Lines:	36524

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💛 - Coveralls