Add function for pairing a Plus-device

[bouwew]

Summary by CodeRabbit

• New Features

  • User-facing support to pair Plus devices with the Plugwise stick.
  • Stick initialization now accepts an additional short init-response format for broader compatibility.

• Bug Fixes / Reliability

  • Improved validation and clearer error reporting during pairing.

• Tests

  • Added comprehensive pairing tests and test data to simulate serial interactions.

• Chores

  • Simplified test runner to run pairing tests directly in non-CI environments.