Optimize byte array operations in Http4sRequestBody

[kciesielski]

This update optimizes how Stream[F, Byte] is handled.

• For StringBody, instead of combining all chunks and copying the entire resulting byte array, I propose body.through(decodeWithCharset(...).compile.string, which decodes incoming byte chunks into smaller Strings, and then collects them efficiently into one final String using fs2's .string.
• More importantly, for InputStreamBody and InputStreamBodyRange, I propose fs2.io.toInputStreamBody(body) to produce a lazily evaluated InputStream instead of fetching all bytes and returning them wrapped in a ByteArrayInputStream.

P.S. Similar optimization to StringBody can be adapted to netty-cats