Fix unsafe Option.get, toString typo, and deprecation warnings

[Copilot]

General improvements to code safety and maintainability.

Bug Fixes

• SourceStage: Replace settings.destination.get with pattern matching to prevent NoSuchElementException. Now fails fast with IllegalArgumentException when destination is missing.
• SourceStage: Fix toString returning "StompClientSink" instead of "StompClientSource"
• JavaConverters: Move wildcard imports to top-level to eliminate deprecation warnings for Scala 2.13+ compatibility

Documentation

Add Scaladoc to public APIs:

• ConnectorSettings parameters and usage semantics
• SendingFrame factory methods
• StompClientSource/StompClientSink materialization behavior and error conditions

Example

Before (unsafe):

connection.subscribe(settings.destination.get, headers.asJava, ...)  // throws if None

After (safe):

settings.destination match {
  case Some(dest) => connection.subscribe(dest, headers.asJava, ...)
  case None => 
    val ex = new IllegalArgumentException("destination is required for StompClientSource")
    promise.tryFailure(ex)
    failStage(ex)
}

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https /usr/lib/apt/methods/https (dns block)
• piccolo.link
  • Triggering command: /usr/bin/curl curl -L REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

improve

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