"text-decoder" dep does not support browsers and is slow

See upstream replies:

* Lack of browser support: https://github.com/holepunchto/text-decoder/issues/8#issuecomment-3897893674
* Performance being not a goal: https://github.com/holepunchto/text-decoder/issues/13#issuecomment-3899552787

It is also untested and did not properly decode UTF-8 until just-released 1.2.6
So this likely needs a dep bump even before replacement

## Performance

That is about 5x slower on UTF-8 in both Node.js and React Native that a fast codepath

See comparison in https://github.com/holepunchto/text-decoder/pull/14

Start by reading the linked upstream replies and the comparison in text-decoder pull request 14, then inspect how streamx uses the text-decoder dependency. Check whether version 1.2.6 addresses UTF-8 correctness; done requires browser support and improved UTF-8 performance in Node.js and React Native.

Written by the indexing model from the issue text.