feat: replace picocli with aesh for CLI parsing

[stalep]

Migrate jbang's CLI framework from picocli to aesh, leveraging aesh's compile-time annotation processor to eliminate runtime reflection and improve startup performance.

Key changes:

• Replace all picocli annotations (@command, @option, @parameters) with aesh equivalents (@CommandDefinition, @GroupCommandDefinition, @option, @argument, @arguments, @OptionList, @OptionGroup, @mixin)
• Convert Callable commands to Command with CommandResult return type
• Port custom type converters, parameter consumers, and preprocessors to aesh Converter and OptionParser interfaces
• Implement external plugin command discovery in help output
• Add default value provider using aesh's post-parse processing
• Wire mutual exclusion validation via aesh's exclusiveWith
• Restore version checking, dynamic completion, option aliases, negatable options, and grouped help sections
• Regenerate native-image configuration for aesh
• Update tests for aesh CLI parsing

Performance (vs picocli, median):

• Native image: 6ms vs 33ms (5.5x faster) for single commands
• JDK 25: 109ms vs 228ms (2.1x faster)
• JDK 11: 149ms vs 269ms (1.8x faster)

[maxandersen]

what is this code actually doing ? first parse command and then an exception occurs and it then runs the actual command?

...remind me why ? :)

[stalep]

parseCommand() gives us direct access to the command instance so we can call doCall() directly and capture the return value — this is what most unit tests need (inspect fields, check exit codes, etc.).

But parseCommand() uses a simplified parsing path that doesn't handle all edge cases (e.g., help requests, parse errors with usage output). When it fails with a CommandLineParserException, we fall back to JBang.execute() which runs through the full aesh runtime and handles those cases properly with correct exit codes and error messages.

In short: fast path for normal commands, fallback to full runtime for error/help scenarios.