Improvement: FindFileOrThrow for dotnet tools caching result between project sessions

Hi, handzlikchris. Thank you for your excellent work.

I noticed that every time project opens, FSR always search deeply into Unity installation path for dotnet tools, which spends seconds to complete. Because of storing in `SessionState`, first-time project launch can't benefit from it.

In my opinion, utilize `EditorPrefs` with `unityVersion` could be better.

Here is my snippet for this:

```csharp
private static string FindFileOrThrow(string fileName)
{
var cacheKey = $"FSR:FilePath_{fileName}:{Application.unityVersion}";
var result = EditorPrefs.GetString(cacheKey, null);

if (result != null && !File.Exists(result))
{
EditorPrefs.DeleteKey(cacheKey);
result = null;
}

if (result == null)
{
result = Directory
.GetFiles(ApplicationContentsPath, fileName, SearchOption.AllDirectories)
.FirstOrDefault();

if (result == null)
{
throw new Exception($"Unable to find '{fileName}', make sure Editor version supports it. You can also add preprocessor directive 'FastScriptReload_CompileViaMCS' which will use Mono compiler instead");
}
}

EditorPrefs.SetString(cacheKey, result);
return result;
}

```

Locate the FindFileOrThrow implementation and inspect how SessionState currently stores the result. Verify the cache is scoped to the Unity version, invalidates missing paths, and avoids the deep search after reopening a project; manually test first launch and subsequent project sessions.

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