Bug: breakpoints are not hit after rebuilding the project [vite]

Related #362

After enabling `sourcemap` for `vite` (see below), I can consistently hit breakpoints, and their locations will be resolved correctly.

```ts
export default defineConfig({
plugins: [sveltekit()], // svelte specific stuff, your config might be different
build: {
sourcemap: true
}
});
```

However, once I rebuild the project (via `vite dev`), breakpoints are no longer hit. No wrong locations, no phantom breakpoints, just not hit at all.

I do wanna stress that rebuilding is something that happens constantly during development, so it should be supported (if possible).

After some investigation, I found out that `vite` appends a timestamp to the sources (and it also keeps old copies), which can be seen in FF's debugger (screenshot below):


I wonder if it's related?

## More info

Launch config:

```jsonc
{
"name": "Launch Firefox",
"type": "firefox",
"suggestPathMappingWizard": true,
"reAttach": true,
"request": "launch",
"url": "http://localhost:5173/",
"webRoot": "${workspaceFolder}"
}
```

The same issue happens on neovim and vscode, so it's not client-side related.