test: add V4 swap ERC20→ERC20 decoder regression test

Adds a test that constructs a Uniswap V4 USDT→USDC swap using
SETTLE/SWAP_EXACT_IN_SINGLE/TAKE sub-actions inside a V4_SWAP command.
Without decodeV4Swap(), the output token would be unresolvable and the
swap name would not show 'USDT → USDC'. This test fails on the old code
and passes with the decodeV4Swap() fix.

Refs: #59

.gitignore

@@ -25,4 +25,3 @@ dist/
 
 # Yarn
 .yarn-integrity
-package-lock.json