#305 - extract calypso-sim into a standalone MQTT simulator crate

[bracyw]

Changes

Pulls the MQTT simulator out of the main calypso binary into its own standalone calypso-sim crate, and deletes the old in-tree src/bin/simulate.rs. The new crate has four input modes — autonomous heartbeat, interactive keymap, scripted replay, and a JSON-RPC stream driver — arbitrated by a per-topic ownership model so the heartbeat doesn't fight a live driver. Also drops the now-unused crossterm dep from the main crate and guards SimValue::initialize against degenerate spec entries (empty min==max range / empty discrete options) so a malformed spec can't panic at startup.

Notes

• calypso-sim is its own workspace (detached Cargo.lock + target dir), so it does not build from a top-level cargo build --all — cd calypso-sim first. See calypso-sim/README.md for all flags, the keymap format, and the stream protocol.
• calypso-sim/src/{simulatable_message,data}.rs are intentional vendored copies of the main crate's files (the sim crate can't depend on calypso). One small documented sim-local divergence: topic_values_inject compiles its {} placeholder regex once instead of per call.
• Heads-up for local checks: the main calypso crate doesn't compile on macOS (it uses socketcan in non-cfg-gated lib code — pre-existing, identical on Develop), so root-workspace clippy/test only pass on Linux/CI. The changed code here is the calypso-sim crate, which passes fmt / clippy -D warnings / test locally.
• Non-blocking follow-ups for later: reconcile a keymap.rs doc-vs-code nit on unit precedence for known topics, and (upstream, then re-vendor) the remaining simulatable_message.rs micro-perf items (rand::rng() reuse).

Test Cases

All assume a broker running (mosquitto) and a viewer (mqttui). From calypso-sim/:

• cargo run -- --list-topics — prints every simulatable topic + unit and exits 0.
• cargo run — autonomous heartbeat; mqttui shows live-looking values updating for every topic that has a sim_freq in the spec. Topics without one are listed once at startup as Warning topics (not simulated): ....
• cargo run -- --enable-topic '^BMS/' — heartbeat publishes only BMS/... topics; --disable-topic '^BMS/' does the inverse (the two are mutually exclusive).
• cargo run -- --key-map manual_sim_keymap.example.json — interactive raw mode; a mapped keypress publishes its topic (random / pinned / increment / sequence per the entry), logging [k] Topic = [..] unit. Ctrl+C exits cleanly.
• cargo run -- --key-map keys.json --script play.txt — replays the script lines (single chars fire keys, sleep N waits), then exits.
• cargo run -- --key-map keys.json --auto — interactive plus background heartbeat; claimed keymap topics override the heartbeat and release back to it afterward.
• cargo run -- --stream then on stdin: {"jsonrpc":"2.0","id":1,"method":"publish","params":{"topic":"Wheel/Buttons/button_id","value":5}} → one-line response {"...","result":{"ts_us":...}} and the message lands on the broker. claim / release / silence / status / list_topics / ping behave per the README table.

Checklist

• No merge conflicts
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• Assign the PR to yourself
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Closes #305