Load multiple files in parallel instead of sequentially

[tmshv]

Problem

src/store/effects/add-multiple-files.ts:4-8 loads files one by one in a for loop:

const addMultipleFiles = createAsyncThunk("addMultipleFiles", async (paths: string[], thunkAPI) => {
    for (const path of paths) {
        thunkAPI.dispatch(addFile(path))
    }
})

When dragging multiple files onto the app, each file waits for the previous one to finish. This creates a poor user experience with large file sets.

What needs to change

Dispatch all addFile thunks in parallel using Promise.all:

const addMultipleFiles = createAsyncThunk("addMultipleFiles", async (paths: string[], thunkAPI) => {
    await Promise.all(paths.map(path => thunkAPI.dispatch(addFile(path))))
})

Note: verify that SourceStorage on the Rust side handles concurrent access safely (it uses Mutex, so should be fine).