[nat] return test stdout & stderr

[scharissis]

It would be nice if TestResult included the stdout & stderr of each test run.

type TestResult struct {
	Metadata types.ValidatorMetadata
	Status   string
	Error    string
	Duration time.Duration // Track test execution time
}

Example stdout of a real test:

stdout of TestSystemWrapETH:

 === RUN   TestSystemWrapETH
time=2025-02-20T08:09:29.878+11:00 level=DEBUG msg="checking balance" wallet=0xa7b30f9e99a248c6d623eaad7bce81217bb84038 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.879+11:00 level=DEBUG msg="checking balance" wallet=0xaff0ca253b97e54440965855cec0a8a2e2399896 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.881+11:00 level=DEBUG msg="checking balance" wallet=0x21dd8d15472844b905e603ddd48a485a630b233b balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.882+11:00 level=DEBUG msg="checking balance" wallet=0xd3f2c5afb2d76f5579f326b0cd7da5f5a4126c35 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.884+11:00 level=DEBUG msg="checking balance" wallet=0x39dc844b8b461c6de6c572cad9585d9f5a8dea6a balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.885+11:00 level=DEBUG msg="checking balance" wallet=0xbb900cf56918a2639daa90c3f7dc5dcd2f5b9935 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.887+11:00 level=DEBUG msg="checking balance" wallet=0x9ef74f0e58fdef70c11e587a45c0a85a3258dcea balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.888+11:00 level=DEBUG msg="checking balance" wallet=0x8e44febeae9c2f2bc89480ae8084328badc496c2 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.890+11:00 level=DEBUG msg="checking balance" wallet=0xf08f610d1956caaab34f18e9e0a122e389496529 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.891+11:00 level=DEBUG msg="checking balance" wallet=0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.892+11:00 level=DEBUG msg="checking balance" wallet=0xb0994e702b603df7191cd68e6544f99126135e34 balance="0 ETH" needed="1 ETH"
time=2025-02-20T08:09:29.894+11:00 level=DEBUG msg="checking balance" wallet=0x15947bf05662cad8df55f004c055939b574f18c0 balance="0 ETH" needed="1 ETH"
    systest.go:161: precondition not met: no available wallet with balance of at least of 1000000000000000000
--- SKIP: TestSystemWrapETH (0.07s)
PASS
ok      github.com/ethereum-optimism/optimism/kurtosis-devnet/tests/interop     (cached)

Note that we have both go test output as well as the actual TestSystemWrapETH logs interleaved.