fix: unused variables in dex_router.rs (amount_out_min, to, deadline, amount_in_max) cause Clippy CI failure

[Pvsaint]

Problem

dex_router.rs has four unused parameter variables:

warning: unused variable: `amount_out_min`  --> dex_router.rs:42
warning: unused variable: `to`              --> dex_router.rs:44
warning: unused variable: `deadline`        --> dex_router.rs:45
warning: unused variable: `amount_in_max`   --> dex_router.rs:74
warning: unused variable: `to`              --> dex_router.rs:76
warning: unused variable: `deadline`        --> dex_router.rs:77

These are stub parameters in the mock DEX router. Since this is intentional stub code, they should be prefixed with _ to silence the warnings.

Acceptance Criteria

• All unused parameters in stub swap functions are prefixed with _ (e.g. _amount_out_min, _to, _deadline)
• A TODO comment is added near each stub function noting what real implementation should do
• cargo clippy --all-targets --all-features -- -D warnings passes for dex_router.rs

Branch & Commit Examples

branch: fix/clippy-warnings-cleanup
commit: fix(dex-router): prefix unused stub parameters with underscore