Do not use saturating_sub for signed types

[gztensor]

Description

1. Get rid of I96F32 in run_coinbase.rs (use U96F32 instead)
2. Avoid using saturating_sub for signed types across code base

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run cargo fmt and cargo clippy to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[JohnReedV]

Convert batch to signed I96F32 to avoid migration of SubnetMovingPrice for now

Should the migration be included in this PR?