[llvm] [lit] Add an option to lit which ratelimits progressbar output. (PR #186479)

[Alexander Richardson via llvm-commits]

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arichardson wrote:

```suggestion
def _float(arg, kind, pred):
    try:
        f = float(arg)
        if not pred(f):
            raise ValueError()
    except ValueError:
        raise argparse.ArgumentTypeError(f"requires {kind} float, but found '{arg}'")
    return f
```
since we depend on modern python, we could use f-strings here to simplify?

https://github.com/llvm/llvm-project/pull/186479