Performance: Avoid database lookup in UserIdKeyResolver for super-user

[AndyButland]

Description

As a small optimization in a particular case - given the super-user's ID and key is known, we can avoid a database look-up. So this PR updates UserIdKeyResolver to do that when this user's ID is looked up from the key, and vice versa.

In passing I also made use of an async method we'd missed, and added documentation to the class and interface.

Change Details

• Avoids unnecessary database lookups when resolving the super-user's ID/key since these are known constants (Constants.Security.SuperUserId and Constants.Security.SuperUserKey)
• Uses ExecuteScalarAsync instead of ExecuteScalar in the async TryGetAsync(int id) method for consistency
  • I removed this, it proved to be the cause of pipeline only integration test failures
• Adds XML documentation comments to IUserIdKeyResolver interface and UserIdKeyResolver implementation

Testing

This can be verified by putting breakpoints in the look-up methods in UserIdKeyResolver to verify that for the built-in admin user, the look-up returns early before the database or cache lookup.

[Copilot]

Pull request overview

This PR optimizes the UserIdKeyResolver service by avoiding unnecessary database lookups for the super-user (whose ID and key are known constants), converting a synchronous database call to async, and adding comprehensive XML documentation.

Key Changes:

• Adds early-return optimization for super-user ID/key resolution to skip database queries
• Fixes async consistency by replacing ExecuteScalar with ExecuteScalarAsync in TryGetAsync(int id)
• Adds XML documentation to both the IUserIdKeyResolver interface and UserIdKeyResolver implementation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Umbraco.Core/Services/IUserIdKeyResolver.cs	Adds interface-level XML documentation describing the service's purpose
src/Umbraco.Infrastructure/Services/Implement/UserIdKeyResolver.cs	Implements super-user optimization checks, fixes async database call, and adds comprehensive XML documentation including class, constructor, and remarks

[Zeegaan]

2 small nitpicks, but overall good idea 💪