Failed Step Rollback

[TanmoySG]

Closes #22

This pull request introduces support for rollbacks in the step processing framework, allowing steps to define rollback functions that execute when a step fails. The changes include new types for rollback state and result, updates to the step execution logic to trigger rollbacks, and modifications to the context and step definitions to track rollback progress and arguments.

Rollback Functionality and Step Execution:

• Added RollbackFunction and RollbackArgs fields to the Step struct, enabling steps to specify custom rollback logic and arguments.
• Introduced the RollbackFn type and new types/constants for RollbackState and RollbackResult to represent the outcome of rollback operations. [1] [2]
• Updated the step execution logic to check for failed steps and invoke the rollback function if defined, including logging and tracking rollback results in the context. [1] [2] [3]

Step Progress Tracking:

• Modified the StepProgress struct and context to include rollback results, and added a method to set rollback progress for a step. [1] [2]

Example Usage and Refactoring:

• Updated the example in example/main.go to demonstrate rollback usage, including a simulated failure and rollback function in the step definition. Also commented out unused code and steps for clarity. [1] [2] [3]

Minor Fixes:

• Fixed import order in example files for consistency. [1] [2]
• Added comments and constants for step and rollback states for better code documentation.

Let me know if you have any questions about how rollback is triggered or tracked in the new implementation!