Handle wp ability run missing input based on input_schema

[Copilot]

wp ability run previously always passed an empty array when no input flags were provided, which caused abilities without an input_schema to fail validation. This PR preserves “no input” as null where appropriate, while keeping compatibility for abilities that do define an input schema.

• Behavior fix: preserve “no input” semantics without breaking object-schema abilities

  • Updated Ability_Command::build_input_with_stdin() to return null when no --input payload or field args are provided.
  • Updated Ability_Command::run() to pass [] instead of null when no CLI input is provided and the ability defines an input_schema.
  • This keeps abilities without input_schema working as intended, while avoiding input is not of type object errors for abilities that require object input.

• Regression coverage: ability without input_schema

  • Extended features/ability.feature with a fixture ability (test-plugin/simple-no-input) that defines no input_schema.
  • Added an execution assertion verifying wp ability run test-plugin/simple-no-input returns [].

// Build phase: null when input is truly absent.
return ( empty( $input ) && null === $json_input ) ? null : $input;

// Run phase: for abilities with input_schema, treat missing input as [].
if ( null === $input && null !== $ability->get_meta_item( 'input_schema', null ) ) {
	$input = [];
}

[codecov]

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[swissspidy]

@copilot fix failing test