[core] Move print_summary from Command to ParseResult

[forfudan]

This PR moves the parsed-argument summary printing utility from Command onto ParseResult, making it callable directly on parse results (and updating examples accordingly).

Changes:

• Added ParseResult.print_summary() (with recursive subcommand printing).
• Removed Command.print_summary(result).
• Updated example CLIs to call result.print_summary().

[Copilot]

Pull request overview

Moves the parsed-argument summary printing utility from Command onto ParseResult, making it callable directly on parse results (and updating examples accordingly).

Changes:

• Added ParseResult.print_summary() (with recursive subcommand printing).
• Removed Command.print_summary(result).
• Updated example CLIs to call result.print_summary().

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/argmojo/parse_result.mojo	Adds print_summary() implementation on ParseResult, including subcommand recursion and unknown-args display.
src/argmojo/command.mojo	Removes the Command.print_summary() helper.
examples/mgrep.mojo	Updates example to call result.print_summary().
examples/mgit.mojo	Updates example to call result.print_summary().
examples/demo.mojo	Updates example to call result.print_summary().

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