feat(bridge): add FetchSnapshot command and SnapshotRegistry (#996)

[Taofik01]

Closes #996

What this PR does

Instead of sending all snapshots upfront, snapshots are now fetched lazily — only when the user clicks a specific step in the UI.

Changes

• internal/bridge/client.go — added FETCH_SNAPSHOT opcode, FetchSnapshot() and FetchSnapshotBatch() functions
• simulator/src/ipc/mod.rs — added SnapshotRegistry, CommandFrame, handle_stdin_command() handler, and FetchResponse frame type

How it works

1. Go bridge writes a FETCH_SNAPSHOT command to the simulator's stdin
2. Simulator looks up the requested snapshot(s) from its in-memory SnapshotRegistry
3. Simulator writes a fetch_response NDJSON frame back to stdout
4. Batch fetching supports up to 5 consecutive frames per request

Acceptance criteria met

• Lazy loading of snapshots works in interactive mode
• Initial simulation result size is reduced (no snapshots sent upfront)
• Batch fetch supports next 5 frames

[dotandev]

fix ci.

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