[Sim] - Custom Topic Injection Mode for Calypso Mock

Description

Extend Calypso's simulation mode to allow specific topics to be selected and run on independent loop intervals, rather than simulating all topics at once.

Acceptance Criteria

• Topics to simulate are specifiable via flags at startup
• Each topic can be assigned its own loop interval (e.g. topic 1 every 30s, topic 2 every 10s)
• Only specified topics are published; all others are excluded
• Invalid topic names fail with a clear error

Proposed Solution

Extend src/bin/simulate.rs, reusing existing MQTT publish and topic generation code. Topics and their intervals are passed as flags. Add tests for topic filtering, per-topic interval behavior, and invalid topic handling.

Mocks

No response