Asset server file watcher is causing stuttering on OSX

## 0.10.0

## \[Optional\] Relevant system information

```
2023-03-23T04:43:00.988197Z INFO bevy_diagnostic::system_information_diagnostics_plugin::internal: SystemInfo { os: "MacOS 13.0.1 ", kernel: "22.1.0", cpu: "Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz", core_count: "8", memory: "64.0 GiB" }
```

## What you did

After upgrading to 0.10 my app started getting slower and slower with every frame while CPU utilization wasn't changing almost at all. None of the cores were fully utilized either. Here is the perf profile suggesting that asset loader might be the bottleneck (updating/freeing function went from few ms to a hundred of ms after first minute).

Flame graph:

Flame graph after turning of file watcher:

Start by reproducing the reported macOS 13 performance degradation with the asset server file watcher enabled, then compare profiling results with the watcher disabled as described in the issue. Done means the progressive frame stuttering and asset-loader overhead no longer occur while the file watcher remains enabled.

Written by the indexing model from the issue text.