Fix ScenarioRunner using methods without result generated by testing/codegen

[tchssk]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes an issue in the ScenarioRunner's method execution template where it was incorrectly handling methods without results. The fix ensures that methods without return values properly return nil as the first return value to match the expected (any, error) signature of the executeMethod function.

• Corrected the template to handle both methods with and without results uniformly
• Added comprehensive test coverage for scenario generation with both result types
• Renamed variables for better clarity between client methods and scenario runner code

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
testing/codegen/testdata/code.go	Renamed variables and added comprehensive test data for scenario runner code generation
testing/codegen/templates/scenario_runner.go.tpl	Fixed template to properly handle methods without results by returning nil as first value
testing/codegen/scenarios_test.go	Added new test file to verify scenario generation for both result and non-result methods
testing/codegen/clients_test.go	Updated variable references to match renamed test data constants

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[raphael]

This is great, thank you!