Simplify QuickGrid OnRowClick rendering by removing conditional duplication

[Copilot]

Simplify QuickGrid OnRowClick rendering by removing conditional duplication

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Address review feedback on QuickGrid OnRowClick implementation

Description

Addresses feedback from #64602 to simplify the RenderRow method by removing duplicated <tr> element rendering.

Changes:

• Coalesce OnRowClick callback into a local variable using EventCallback.Factory.Create
• Remove if/else block that duplicated the entire <tr> element
• Always pass @onclick to the row—RenderTreeBuilder.AddAttribute already elides the attribute when the callback has no delegate

var rowClick = OnRowClick.HasDelegate 
    ? EventCallback.Factory.Create<MouseEventArgs>(this, () => OnRowClick.InvokeAsync(item)) 
    : default;

<tr @key="@(ItemKey(item))" aria-rowindex="@rowIndex" class="@combinedClass" @onclick="@rowClick">

Fixes #64602

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