Optimize the shopping cart page by avoiding the first flash after user interaction.

### Description

On your shopping page that you showed to the reader: https://amp.dev/documentation/examples/e-commerce/shopping_cart/ I tested it and noticed that after the first interaction(click on a specific add or subtract button) , there is a visual flash. This flash is only observed after the first interaction, but not after When the cart data needs to be updated in the cartitemlist state.

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But this makes the user experience unpleasant or frustrating. And I have an effective method to avoid that.

### Alternatives Considered

Now, to avoid this problem, I initialized the data with AMP state via SRC from the remote source. For example...

During loading, the data will be automatically inserted into the cartitemlist state. If the user clicks any button, this updates the src file more quickly without displaying any flashing.

### Additional Context

_No response_

Start with the shopping cart example at https://amp.dev/documentation/examples/e-commerce/shopping_cart/ and inspect the amp-state cartItemsList initialization and the first add or subtract interaction. Reproduce the initial visual flash, then verify that the example no longer flashes after the first interaction while cart data updates.

Written by the indexing model from the issue text.