amazon-location-service: uvx mcp-proxy-for-aws@latest causes unbounded uv cache growth

### Summary
The `amazon-location-service` plugin launches its MCP server with `uvx mcp-proxy-for-aws@latest`. Every Copilot CLI session that loads the plugin creates a fresh ephemeral `uvx` environment cached under `~/.cache/uv`. These ~110 MB environments accumulate without bound because `@latest` re-resolves each launch and nothing prunes them.

### Impact
On my machine the uv cache grew to **138 GB** (~1,250 cached environments, 9.1M files) before I noticed. `uv cache clean` reclaimed 117 GiB.

### Config
```json
{
"mcpServers": {
"aws-mcp": {
"command": "uvx",
"args": ["mcp-proxy-for-aws@latest", "https://aws-mcp.us-east-1.api.aws/mcp"]
}
}
}
```

### Environment
- macOS (arm64), uv 0.7.2, GitHub Copilot CLI
- Plugin: `amazon-location-service@agent-plugins-for-aws` v1.0.0

Locate the amazon-location-service plugin definition and inspect how its MCP server command is configured. Reproduce the uvx invocation or review its cache behavior, then verify that repeated plugin sessions no longer create unbounded cached environments and that the plugin still connects to the AWS MCP endpoint.

Written by the indexing model from the issue text.