fix: Empty and loading template doesn't span columns in FluentDataGrid

[JamesNK]

🐛 Bug Report

The empty and load templates aren't spanning header columns when the mode is Table:

1. Clone https://github.com/dotnet/aspire.git
2. Switch to jamesnk/grid-table-display branch
3. Open Aspire.slnx
4. Run the TestShop.AppHost project that is in the playground folder
5. Go to traces/structured logs pages and enter filter to make data grid not show any data

🤔 Expected Behavior

Template should fill the width of the data grid.

😯 Current Behavior

No span

💁 Possible Solution

🔦 Context

🌍 Your Environment

• OS & Device: [e.g. MacOS, iOS, Windows, Linux] on [iPhone 7, PC]
• Browser [e.g. Microsoft Edge, Google Chrome, Apple Safari, Mozilla FireFox]
• .NET and Fluent UI Blazor library Version [e.g. 8.0.2 and 4.4.1]