forge-stream — add test verifying extend_stream() increases remaining tokens and get_stream_status() reflects new end_time

[Austinaminu2]

Summary

extend_stream() is implemented but there are no tests for it in the current codebase. Given it transfers additional tokens and modifies end_time, it needs comprehensive coverage.

Tasks

• Create a stream with rate=100, duration=1000 (total=100,000)
• At t=500 (halfway), extend by 500 additional seconds
• Assert get_stream().end_time equals original end_time + 500
• Assert get_stream_status().remaining now reflects the extended total
• Advance to original end time — verify stream is still active
• Advance to new end time — verify is_finished = true
• Verify sender's token balance decreased by additional_seconds * rate at extension time
• Add tests for: extending a cancelled stream (reverts), extending after end_time (reverts), additional_seconds = 0 (reverts)

Labels: testing, forge-stream