Add middleware between stages to validate CommandContext state

[drewburlingame]

Add middleware between pipeline stages to validate CommandContext is exiting a stage with required data populated.

Details:

• ParseResult should be fully populated after Parse stage
• Invocation contexts should be fully populated after BindValues stage
• When ctor options are moved to a middleware method, invocation context should be populated in Parse stage

Location: CommandDotNet/AppRunner.cs:154

Context: This would improve debugging and diagnostics by catching configuration issues early in the pipeline.