Refactor error handling and improve exception messages across multiple admin commands

[gautamdsheth]

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Type

• Bug Fix
• New Feature
• Sample

Related Issues?

Fixes #X, partially fixes #Y, mentioned in #Z, etc.

What is in this Pull Request ?

Please describe the changes in the PR.

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[Copilot]

Pull Request Overview

This PR refactors error handling and improves exception messages across multiple admin commands by modernizing null checks, updating exception types for better semantic accuracy, replacing string formatting with string interpolation, and applying C# collection expression syntax where appropriate.

• Modernizes null validation using ArgumentNullException.ThrowIfNull() instead of traditional if-null-throw patterns
• Updates exception types to be more semantically appropriate (e.g., InvalidOperationException instead of ArgumentNullException for operational failures)
• Replaces string formatting with string interpolation for cleaner, more readable code

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Tests/PnP.PowerShell.Tests.csproj	Updates target framework from .NET 6.0 to .NET 8.0
src/Commands/Utilities/REST/RestHelper.cs	Modernizes string formatting using string interpolation
src/Commands/Utilities/DynamicLinq.cs	Replaces manual null checks with ArgumentNullException.ThrowIfNull()
src/Commands/SiteDesigns/SetBuiltInSiteTemplateSettings.cs	Refactors null check and adds required System import
src/Commands/SiteDesigns/GetBuiltInSiteTemplateSettings.cs	Refactors null check and adds required System import
src/Commands/AzureAD/RegisterAzureADApp.cs	Replaces resource strings with inline error messages
src/Commands/AzureAD/NewAzureADGroup.cs	Updates confirmation message to use string interpolation
src/Commands/Apps/GetAzureADAppSitePermission.cs	Optimizes list initialization with capacity
src/Commands/Apps/GetApplicationCustomizer.cs	Modernizes list initialization with collection expression
src/Commands/Admin/SetTenantSyncClientRestriction.cs	Improves error message with inline string interpolation
src/Commands/Admin/SetTenant.cs	Optimizes list initialization with capacity
src/Commands/Admin/RemoveTenantSyncClientRestriction.cs	Modernizes list initialization with collection expression
src/Commands/Admin/RemoveTenantSite.cs	Updates confirmation message using string interpolation
src/Commands/Admin/GetTenantDeletedSite.cs	Modernizes list initialization and improves exception types
src/Commands/Admin/GetStorageEntity.cs	Optimizes list initialization with capacity
src/Commands/Admin/GetContainerTypeConfiguration.cs	Improves exception type and error message
src/Commands/Admin/AddTenantRestrictedSearchAllowedList.cs	Updates exception type for better semantic accuracy

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