Fixes for non-blocking edge cases

[dgarske]

• Fixes for non-blocking publish with payload larger than maximum TX buffer. ZD 16769
• Fixes for write non-blocking (would block) edge cases.
• Fix for write position on cancel of message in progress.
• Added check for zero return on read, which is a compatibility layer indicator for disconnect.
• Added write WOLFMQTT_TEST_NONBLOCK support.
• Fix to make sure ctrl+c is honored during a want read/write case.
• Fix the firmware update example to properly synchronize publish and use a unique topic name.
• Improve multi-thread test message to use larger size (> tx but) and in test mode check for actual message.
• Improve remote test done logic.
• Only run GitHub CI for PR's, not local push.
• Properly set WOLFMQTT_NO_EXTERNAL_BROKER_TESTS for each test.
• Use cat for logs, not more.