Updated flow utils generate flow stack

[ninokeldishvili]

Motivation

Porting legacy tests from ".FlowERC20/flowTime" — test case "should support gating flows where a flow time has already been registered for the given id"

Solution

Add new test written in foundry

Checks

By submitting this for review, I'm confirming I've done the following:

• [x] made this PR as small as possible
• [x] unit-tested any new functionality
• [x] linked any relevant issues or PRs

Dependencies

• [ ] #179
• [x] #70