fix: Remove incorrect amount propagation in exact output swaps

[VolodymyrBg]

Related Issue

Which issue does this pull request resolve?
This PR fixes a critical issue in the V4Router's _swapExactOutput function
where amounts were incorrectly propagated in multi-hop trades

Description of changes

The bug was
caused by unnecessarily setting amountOut = amountIn in each iteration, which
led to incorrect calculations for subsequent hops.

• Removed the line amountOut = amountIn from the _swapExactOutput function
• Maintains correct output amount throughout the path traversal
• Ensures accurate input amount calculations for each hop

This fix prevents:

• Incorrect slippage calculations in multi-hop trades
• Potential trade failures due to amount mismatches
• Inaccurate price impact calculations