Add support for keyed DI and update target frameworks

[Chris-Wolfgang]

Resolves #552 and #558

Introduced FromKeyedServicesAttribute for resolving services by key in method parameters. Updated ReflectionHelper to handle keyed service resolution using IKeyedServiceProvider. Added tests to validate this functionality.

Upgraded target frameworks to net8.0 across projects and updated test to target 8.0 and 9.0. Simplified reflection code by replacing Array.Empty<object>() with []. Updated dependencies to use Microsoft.Extensions.DependencyInjection.Abstractions and newer versions of related packages.

Enhanced test coverage with new tests for keyed DI and fixed typos in test method names. Adjusted project files to include additional package references and modernized exception messages for consistency.

[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.74%. Comparing base (5053c19) to head (1bc5c0b).

Files with missing lines	Patch %	Lines
src/CommandLineUtils/Internal/ReflectionHelper.cs	70.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #560      +/-   ##
==========================================
- Coverage   77.79%   77.74%   -0.05%     
==========================================
  Files         104      104              
  Lines        3333     3339       +6     
  Branches      728      731       +3     
==========================================
+ Hits         2593     2596       +3     
- Misses        580      581       +1     
- Partials      160      162       +2     

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[natemcmaster]

Thanks @Chris-Wolfgang . I pushed some updates to get this change to build with GitHub CI to validate it works.

The main library currently has no external package dependencies. Adding Microsoft.Extensions.DependencyInjection.Abstractions as a hard requirement would force all users to take this dependency, even if they don't use DI, and break the "minimal dependencies" philosophy of the core library.

What do you think about some of these alternatives?

Option 1: Reflection-based detection

Use reflection to detect if the keyed services types are available at runtime, without a compile-time dependency. The feature works automatically when users have the DI abstractions available; otherwise it's silently ignored (or throws a clear error only when someone actually uses [FromKeyedServices]).

Pros: No new dependencies, works if user brings their own DI
Cons: More complex code, potential runtime performance overhead (can be mitigated with caching)

Option 2: Separate package

Create a new package like McMaster.Extensions.CommandLineUtils.DependencyInjection that provides the keyed services integration, similar to how Hosting.CommandLine works.

Pros: Clean separation of concerns
Cons: Users need an additional package for keyed DI

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I'm inclined toward Option 1 since it preserves the zero-dependency nature of the core library while still enabling the feature for users who have the DI abstractions. What do you think?