Enhance error handling, documentation, and safety checks

[AlienDwarf]

Testing and Multithreading Reliability:

• Refactored the stress test to use a RwLock<Option<HeavyFn>> instead of OnceLock, ensuring thread-safe access and mutation of the trampoline function and improving test stability in multithreaded scenarios.

Instruction Relocation and Disassembler Enhancements:

• Changed Disassembler to be pub(crate) for encapsulation, and improved instruction length calculation to handle cases where min_size exceeds typical buffer sizes

IAT Hook Robustness and Error Handling:

• Improved error handling in IAT hook restoration: ensures the original function pointer is restored if VirtualProtect fails, and returns a more accurate error.
• Updated string reading from RVA to use String::from_utf8 for stricter UTF-8 validation.