Keep wasm download feedback active through module initialization

[MUFFANUJ]

Fixes #46 by wrapping Cockle’s wasm download callback in the terminal worker so the visual feedback stops only after the loaded Emscripten module factory resolves, covering the actual wasm fetch and initialization phase while preserving existing behavior for non-wasm modules.

[github-actions]

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[ianthomas23]

Thanks for looking into this, but I don't think this is something I want to proceed with.

I have come to the conclusion that I don't like my original idea of reporting the download within the terminal itself, it is too invasive and differs too much from that which occurs in a real terminal. I am leading towards removing the download tracker from cockle and instead replacing it with a more generic system of a Signal emitted when a command downloads, starts running and completes, which clients can choose to connect to if they wish. This covers other use cases as well as the download feedback. As to how this might surface in the terminal UI I am not sure yet; probably some text in the status bar which is similar to that displayed by kernels.