[FEATURE] Add Uniswap swap benchmark test

[chatton]

Problem to solve

No benchmark test for realistic DeFi workload throughput.

Proposed solution or feature

Add TestUniswapSwaps using spamoor's uniswap-swaps scenario (~150K+ gas/tx). Measures throughput under a realistic DeFi workload.

Alternatives considered

N/A

Additional context

Part of #2288.