fix(streaming): resolve word concatenation in streaming output rails (#1259)

* fix(streaming): resolve word concatenation in streaming output rails

- fix spacing loss in streaming output where words were concatenated without spaces
- refactor BufferStrategy interface with ChunkBatch named tuple for better API design
- improve variable names and add comprehensive Google-style documentation
- add robust exception handling for streaming generation tasks
- enhance test coverage
- remove unnecessary chunk splitting that defeated buffer strategy purpose

Fixes issue where `test_sequential_streaming_output_rails_allowed` failed due to
output like "safeand complianthigh quality" instead of "safe and compliant high quality".

The root cause was in `_run_output_rails_in_streaming` calling `split()` on chunks
that already had proper spacing, then failing to reconstruct the original format.

Author: Pouyanpi