Harnesses verifying slice types for add, sub and offset

[szlee118]

Towards #76

Changes

Contracts Added:

• Added contracts for <*mut T>::add, <*mut T>::sub, and <*mut T>::offset operations for raw pointers to slices.

Proofs Implemented:

• Added proofs for the above contracts, verifying safety for the following slice pointee types using arrays:
• All integer types (i8, i16, i32, etc.).
• Tuples (composite types) (e.g., (i8, i8), (i32, f64, bool)).
• Unit type (()).

Macro Definitions:

• Introduced macros to simplify and automate harness generation:
• One macro for add and sub operations on slices.
• Another macro for offset operations on slices.

Array-Based Implementation for Slice Verification:

• Arrays are used as a proxy for slices (as slices do not have a known length at compile time) to enable proper bounds checking and assumptions during verification.

This should be merged after another PR for dependency issues.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[szlee118]

@feliperodri FYI