Fix `Trace::HttpIO` can not render multi-byte chars

What does this MR do?

This MR fixes

• HttpIO can't read multi-bytes chars because it slices characters by length method. We need to use byteslice over slice and bytesize over length.

Note:

• The test case is covered by updating spec/fixtures/trace/sample_trace. It contains multi-byte characters, also it was extracted from the actual build log from CE pipelines, so the rspec result is more accurate than ever. All specs in ci/trace/http_io_spec.rb uses fixtures/trace/sample_trace with various excercise. So we don't need to add additional tests.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #44981 (closed)