Fix fault injection crash

[Alan-Jowett]

This pull request includes several changes to the src/ke.cpp file, focusing on improving the handling of the threadpool callback environment by using std::optional and making minor formatting adjustments.

Improvements to threadpool callback environment handling:

• Included the <optional> header and changed the TP_CALLBACK_ENVIRON variable to use std::optional for better management of its initialization state. [1] [2]
• Updated the initialization and cleanup logic for the threadpool callback environment to use std::optional methods, ensuring proper resource management. [1] [2] [3]

Formatting and minor code adjustments:

• Added or adjusted function definitions and bodies to follow a consistent style, improving readability. [1] [2] [3] [4] [5] [6]
• Removed unused variable threadpool_environment_initialized from the usersim_initialize_irql function.
• Ensured the CreateThreadpoolTimer function call uses the value() method of std::optional for the threadpool callback environment.