Revise "ACKs with commands #yd3" (stage 57)

[TropicolX]

Removed unnecessary details section and streamlined explanations about offset tracking and command processing.

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Note

Streamlines the replication stage doc with a concise ACK/offset explanation, normalized examples, and an explicit RESP array response requirement.

• Docs (stage_descriptions/replication-15-yd3.md):
  • Add an ACKs recap and replace the collapsible details with concise offset-tracking guidance, emphasizing that the current REPLCONF GETACK * is excluded.
  • Revise examples/tests: normalize command casing (REPLCONF, PING, SET), streamline comments, and update byte-offset calculations.
  • Clarify that replicas count bytes for all propagated commands, and keep the PING behavior note.
  • Add an explicit requirement that REPLCONF ACK <offset> be returned as a RESP array; remove redundant/extraneous notes.

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