refactor broker and dealer into their own packages under router

[gammazero]

• Move dealer to router/dealer
• Move broker to router/broker

Description, Motivation and Context

• Better organize router code
• Provide separation of broker and dealer concerns
• Allow Broker and Dealer to be used as independent packages for other router implementations

What is the current behavior?

broker and dealer were part of router package.

What is the new behavior?

broker and dealer are in their own packages.

What kind of change does this PR introduce?

• Enhancement (improve existing code or documentation without affecting behavior)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• I have added tests to cover my changes.
• Overall test coverage is not decreased.
• All new and existing tests passed.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.