Align LinuxStrategy async pattern with WindowsStrategy

[Copilot]

LinuxStrategy used Execute() with Task.Run() wrapper while WindowsStrategy implemented ExecuteAsync() directly, creating inconsistent async patterns across platform strategies.

Changes

• LinuxStrategy.cs: Replace Execute() + Task.Run() with native ExecuteAsync() implementation

  • Remove fire-and-forget Task.Run() wrapper
  • Update error messages to reference correct class name (was incorrectly referencing WindowsStrategy)

• GeneralUpdateBootstrap.cs: Fix compilation error from previous commit

  • Store GetOption(UpdateOption.DownloadTimeOut) result to avoid duplicate calls
  • Use ternary operator for zero check (value types return 0 as default, not null)

Both platform strategies now follow identical async patterns:

// Before
public override void Execute()
{
    Task.Run(async () => { /* async work */ });
}

// After  
public override async Task ExecuteAsync()
{
    /* async work */
}

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[Copilot]

Pull request overview

This PR aligns the async implementation patterns between platform strategies and fixes a compilation error in the bootstrap configuration. The LinuxStrategy previously used a fire-and-forget Task.Run() pattern while WindowsStrategy properly implemented ExecuteAsync(), creating inconsistent behavior where LinuxStrategy's Execute() would return immediately without waiting for async operations to complete.

Key Changes

• Refactored LinuxStrategy from fire-and-forget Execute() + Task.Run() to proper async Task ExecuteAsync() implementation
• Corrected error message references from "WindowsStrategy" to "LinuxStrategy" in error logging
• Fixed compilation error in GeneralUpdateBootstrap by properly handling value-type default (0) instead of using null coalescing operator for timeout configuration

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/c#/GeneralUpdate.Core/Strategys/LinuxStrategy.cs	Refactored to use native async/await pattern, removed fire-and-forget wrapper, and corrected class name references in error messages
src/c#/GeneralUpdate.Core/GeneralUpdateBootstrap.cs	Fixed timeout option handling to check for default value (0) instead of null, as GetOption returns non-nullable int

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