Implemented `SegmentedWriter`

[streamich]

Now when Writer runs out of space, it allocates a new 2x larger buffer an copies all the memory. Instead implemented as SegmentedWriter:

• SHOUL implement the same public API: class SegmentedWriter implements Writer.
• Introduce segments in the writer, distinct disjoint buffers. When SegmentedWriter runs out of space it allocates a new segment, which is 2x larger than the last un-flushed segment in the buffer. The segment is appended to the segment list this.segments.push(u8), not concatenated bit buffered data.
• Join the buffers only on .flush().
• The .x (and other public APIs) should still work the same as in Writer.
• Take special care to test methods that operate across segment splits.