Fix "bufio.Scanner token too long" error by replacing Scanner with Reader in SSE

[yudgnahk]

Related issues:

• Opencode stuck after token too long #3409
• bufio.Scanner: token too long #3502
• Fix "bufio.Scanner token too long" error by replacing Scanner with Reader in SSE #3506

Fix bufio.Scanner token too long error in SSE decoder

The SSE stream decoder was hitting a 32MB hard limit when processing large events,
causing bufio.Scanner: token too long errors. This blocked users from reading large
files through the TUI.

Changes:

• Register UnboundedDecoder for the text/event-stream

    ssestream.RegisterDecoder("text/event-stream", decoders.NewUnboundedDecoder)

• Uses ReadBytes('\n') which grows dynamically without size limits
• Added documentation and test files

Testing: Verified with events up to 50MB. All tests pass.

[yudgnahk]

Hey @rekram1-node, this is my PR.
It's a pleasant if you help me review it.
Thank you!

[yudgnahk]

Hi @rekram1-node,
Maybe you forgot this PR?...

[rekram1-node]

will take a look, today I got the most github notifications ive ever had so a few things may slip through

I didnt forget about u tho! Just hadnt had a chance to review