[Feature]: Large files: virtualization and progress  #78

What type of issue is this?

• Bug report
• Feature request

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of the reqifviewer
• I have searched open and closed issues to ensure it has not already been reported

Description

Acceptance criteria

• A large sample (for example 10,000 spec objects) is added to the test data; loading shows progress; tree, document and table views stay responsive (virtualized).

Steps to Reproduce

NA

System Configuration

• reqifviewer version: 6.1.0 (development, with [Refactor] Blazor Blueprint app shell and Blazor Web App hosting #56)
• Environment (Operating system, version and so on): Windows 11, Chrome
• .NET Framework version: .NET 10
• Additional information: Plan item R-12 of the viewer improvement plan. Size: M.