fix(network): enforce RFC-compliant SASL authentication

[mbuckton]

Summary

• allowlist SCRAM-SHA-256 and PLAIN at the server boundary
• require SSL, DTLS, or WSS before accepting PLAIN
• require exact MQTT enhanced-auth method names and client-first authentication data
• enforce authorization identity equality, exchange limits, and post-close rejection
• dispose SASL state from MQTT 5, MQTT-SN 2, and AMQP protocol lifecycles
• migrate server test clients and endpoint configuration from CRAM-MD5/SCRAM-SHA-512 to SCRAM-SHA-256

Tests

• server mechanism allowlist and protected-transport policy
• callback ordering and authorization identity rejection
• existing MQTT 5 and MQTT-SN integration clients updated for client-first SCRAM-SHA-256
• focused Java 21 compilation of the SASL boundary
• end-to-end SCRAM-SHA-256 and protected PLAIN exchanges through the server wrapper

Depends on Maps-Messaging/authentication_library#465.

Full Maven resolution was unavailable in the managed environment because the project depends on Maps/private build artifacts.

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