Fix Documentation and Minor Code Corrections

[zeevick10]

This pull request addresses several documentation issues and minor code corrections across multiple files. Key changes include:
Documentation Updates:

1. Clarified the usage of the get_builtin_costs function in the README file, ensuring that users understand the implications of gas checks and the necessary modifications to the poseidon_hash_span function.

Code Corrections:

1. Fixed comments in the fq.cairo file to accurately describe the modular inverse calculation.
2. Updated the address reference in the dict_write function within dict_hint_utils.rs for clarity.
3. Removed redundant comments in the vm_core.rs file to streamline the code.

These changes aim to improve the clarity and maintainability of the codebase.