Fix integer widths

[Alan-Jowett]

This pull request includes changes to the vm/ubpf_instruction_valid.c file to improve type safety and consistency in the _initialize_lookup_table and _in_range functions.

Improvements to type safety and consistency:

• vm/ubpf_instruction_valid.c: Changed the loop variable type from int to size_t in the _initialize_lookup_table function to ensure proper handling of the loop index.
• vm/ubpf_instruction_valid.c: Updated the parameter types in the _in_range function from int to int32_t for better consistency and clarity.

[coveralls]

coverage: 79.201%. remained the same
when pulling 5ef0f8c on Alan-Jowett:use_correct_width
into 3c639e6 on iovisor:main.