Revise "Configure listening port" (stage 43 - #bw1)

[TropicolX]

Updated the stage description to include details about custom port support for the Redis server and clarified the testing process.

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Note

Revamps the replication stage docs to explain leader-follower replication and clearly document --port usage, defaults, and test behavior.

• Docs: Update stage_descriptions/replication-01-bw1.md
  • Replication overview: Adds concise explanation of leader-follower replication.
  • Custom port support: Documents --port flag usage, example invocation, default to 6379, and starting TCP server on specified port.
  • Tests section: Clarifies that the tester connects to the provided port without relying on the example value.
  • Notes cleanup: Removes redundant default-port note; retains guidance on random ports and script arg forwarding.

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