Fix liquidity_abs undefined behavior

[gztensor]

Description

liquidity_delta.abs() panics on i64::MIN

• File: pallets/swap/src/pallet/impls.rs
• Severity: Low
• Status: Confirmed

liquidity_delta.abs() on a user-supplied i64 panics in debug / overflow-check builds when the value is i64::MIN. In production WASM release builds, wrapping semantics cause the value to fail the ensure check harmlessly. No production impact, but the code is undefined behavior-adjacent in debug builds.

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 ./scripts/fix_rust.sh 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