Improve std.uni:toCase performance

[rikkimax]

For the benchmark that Serg pointed me at as being slow, it went from 26ns down to 7ns.

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[xoxorwr]

For the benchmark that Serg pointed me at as being slow, it went from 26ns down to 7ns.

Can you share the benchmark?

[rikkimax]

For the benchmark that Serg pointed me at as being slow, it went from 26ns down to 7ns.

Can you share the benchmark?

The fork with the D code: https://github.com/cyrusmsk/mojo-unicode/tree/dlang_bench