Rename T variable to sim_horizon for clarity

[phumthep]

Issue Description

Currently, the variable T is used throughout the power system modeling package to represent the simulation horizon (the total number of time steps in the simulation). This single-letter variable name can be confusing and doesn't convey its meaning clearly

Proposed Change

Refactor the code to replace all instances of the variable T with the more descriptive name sim_horizon. This change will improve code readability and maintainability by making the purpose of the variable immediately clear

Tasks

• [ ] Replace T with sim_horizon throughout the workspace
• [ ] Update documentation and comments. Ensure any references to T in documentation or code comments are updated accordingly