Optimize counting digits in line numbers during error reporting further

[llogiq]

This one-ups #82248 by switching the strategy: Instead of dividing the value by 10 repeatedly, we compare with a limit that we multiply by 10 repeatedly. In my benchmarks, this took between 50% and 25% of the original time. The reasons for being faster are:

1. While LLVM is able to replace a division by constant with a multiply + shift, a plain multiplication is still faster. However, this doesn't even factor, because
2. Multiplication, unlike division, is const. We also use a simple for-loop instead of a more complex loop + break, which allows
3. rustc to const-fold the whole loop, and indeed the assembly output simply shows a series of comparisons.

[rust-highfive]

r? @oli-obk

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[oli-obk]

@bors r+

now if we only had perf tests for failing programs 😆

[bors]

📌 Commit 8abc5fd has been approved by oli-obk

[bors]

⌛ Testing commit 8abc5fd with merge 35dbef2...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 35dbef2 to master...