Replace `.format()` with f-strings

[ben05allen]

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This issue aims to improve the readability and performance of the codebase by replacing .format() method calls with f-strings.

Python 3.6 introduced f-strings (formatted string literals), which provide a more concise and readable way to format strings compared to the .format() method. F-strings are also generally faster.

Identify all instances of .format() in the codebase and refactor them to use f-strings.

Notably, the LineWriter class in write.py uses .format() as the base of its template.

As the oldest Python version supported is 3.8, there is no need to retain .format().

[e-io]

There are only five ".format" calls total in the project:

So, it would not be difficult to replace them with modern f-strings.

[roskakori]

Looks good, feel free to assign and implement this any time.