Only send the delta on the partial tool call

[rumpl]

Only sends the delta arguments received on each partial tool call. We used to send the whole accumulated tool call arguemnts, which is dumb, the clients should handle accumulation if they care.

Also added sending the tool definition only on the first partial too call

[rumpl]

/review

[docker-agent]

Assessment: 🟢 APPROVE

This PR correctly implements delta-only transmission for partial tool call events. The changes include:

1. Normalization logic in streaming.go that correctly detects whether providers send full buffers or deltas by checking if the new chunk starts with the accumulated buffer
2. Delta extraction that properly calculates the new bytes and updates the accumulated state
3. TUI component updates that accumulate deltas when status is "pending"
4. Comprehensive tests verifying both delta-only and full-buffer normalization scenarios

The code correctly handles:

• Providers that send true deltas (concatenates to accumulated buffer)
• Providers that resend full buffers (detects prefix, extracts delta, updates buffer)
• First event emission with tool name and definition
• Subsequent events with only argument deltas (no definition)
• Proper accumulation in TUI components

No bugs found in the changed code.

[rumpl]

I'm not so sure about the normalization in streaming.go, I'll remove it, it doesn't make sense