Update Inputs library return types to match VM specs

[bitzoic]

Description

There have been changes to the VM specs where the return type has been updated from u16 to u64 or from u8 to u16 for inputs. These changes are now reflected in the std-lib's Inputs library. Specs: https://github.com/FuelLabs/fuel-specs/blob/master/src/tx-format/input.md

Closes #6107

Breaking

This is a breaking change. Any use of the following will need to be updated:

• input_count() now returns a u16
• input_witness_index() now returns a Option<u16>
• input_predicate_length() now returns a Option<u64>
• input_predicate_data_length() now returns a Option<u64>
• input_message_data_length() now returns a u64

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.