Fix reading CompressedSegmentation with uint32 data

[fm3]

The old code padded every 32-bit output value with another 32 zeroes due to the to-long conversion.

As mentioned in #6947 we didn’t have a uint32 test dataset yet when implementing this.

I also removed some superfluous parentheses.

Steps to test:

• Import neuroglancer precomputed dataset with compressed uint32 segmentation, e.g. from https://scm.slack.com/archives/C5AKLAV0B/p1713253591614229
• Segmentation should look plausible

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• Updated changelog
• Needs datastore update after deployment

[normanrz]

nice!