This update creates a shared way to settle customer accounts in point of sale test tours and reuses it across existing scenarios. It helps keep customer selection and payment flow consistent when dialogs are closed and reopened, reducing the chance of test failures or missed customer data.

In this commit:
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- We have introduced a common function for settlement of customer accounts and replaced it in existing tours.

task: 5028009
related PR: [95156](https://github.com/odoo/enterprise/pull/95156)