Switch back to building for size

[sophiajt]

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[aminya]

@jntrnr I don't think it is a good idea to use z. z turns of the loop vectorization, which means no SIMD usage, which is a huge performance hit. You should at least use s if you want.

Turning on LTO, would probably also reduce the size.

I recommend that you build nu binary with all the optimizations, and instead build less used plugins and binaries for size.