Eliminate most str.format() and %-formatting

[hynek]

Micro-optimization is the root of all success.

[hynek]

This btw gives us ~6% performance gain on class creation for simple classes, just by being more idiomatic (and getting rid of the mistake called format).

Measured using:

def create(loops):
    range_it = range(loops)
    d = attrs.define

    t0 = pyperf.perf_counter()

    for _ in range_it:
        @d
        class C:
            a: int
            b: int

    return pyperf.perf_counter() - t0

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I presume that more complex classes give us even bigger gainzzz.