Use `procref` for FPI tutorials

### Feature description

Instead of string formatting, we should use `procref` opcode for FPI tutorials.

### Why is this feature needed?

Code clarity.

### Motivation

https://github.com/0xMiden/miden-base/pull/1883#discussion_r2349184113

Look at the linked PR discussion to understand the context of using `procref` opcode instead of string formatting in FPI tutorials. Examine the tutorial files in the repository to find where FPI (Foreign Procedure Interface) examples are currently using string formatting. Replace those instances with the `procref` opcode as specified, ensuring the tutorials still compile and run correctly.

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