test: use equality in the withdraw multiple test and in invariant

[andreivladbrg]

As we changed the sd to 18 decimals, I discovered that the delay explained in the technical doc no longer holds true. The issue that prevented us from identifying the fix earlier was that these tests were giving false positives due to descaling the ongoing debt back to the token's decimals.

For example, previously, if the withdrawable amount was 1.99 tokens, the recipient would withdraw 1 token, and the snapshot debt would remain 0, causing a delay for the remaining 0.99 tokens. Now, with the snapshot updated to 0.99, thus there is no delay which is proven by the new test in this branch:

flow/tests/integration/concrete/withdraw-delay/withdrawDelay.t.sol

Lines 10 to 47 in bc6643b

	function test_Withdraw_NoDelay() external {
	// 0.001e6 USDC per day
	uint128 rps = 0.000000011574e18;
	vm.warp(OCT_1_2024);
	uint256 streamId = flow.createAndDeposit(users.sender, users.recipient, ud21x18(rps), usdc, true, 0.001e6);
	uint40 initialSnapshotTime = OCT_1_2024;
	assertEq(flow.getSnapshotTime(streamId), initialSnapshotTime, "snapshot time");
	// Assert that there is still only one token unlocked.
	vm.warp(initialSnapshotTime + 172 seconds);
	assertEq(flow.withdrawableAmountOf(streamId), 1);
	// Warp to the second when the second token gets unlocked.
	vm.warp(initialSnapshotTime + 173 seconds);
	assertEq(flow.withdrawableAmountOf(streamId), 2);
	// Warp one second back in time, to test if there is a delay.
	vm.warp(initialSnapshotTime + 172 seconds);
	// Withdraw the token.
	(uint128 withdrawnAmount,) = flow.withdrawMax(streamId, users.recipient);
	assertEq(withdrawnAmount, 1, "withdrawn amount");
	// Test the second gets unlocked, which proves there is no delay.
	vm.warp(initialSnapshotTime + 173 seconds);
	assertEq(withdrawnAmount + flow.withdrawableAmountOf(streamId), 2);
	// Warp to a second before the third token gets unlocked.
	vm.warp(initialSnapshotTime + 259 seconds);
	assertEq(withdrawnAmount + flow.withdrawableAmountOf(streamId), 2);
	// Warp to the second when the third token gets unlocked.
	vm.warp(initialSnapshotTime + 260 seconds);
	assertEq(withdrawnAmount + flow.withdrawableAmountOf(streamId), 3);
	}

[smol-ninja]

Excellent observation @andreivladbrg. Left some comments below.

[smol-ninja]

Good to go. I left a comment below in case you want to address it.