fix: enable optimistic select by default

[achingbrain]

If only one protocol is specified, send it with the first data block to skip the mss round-trip tax.

Change checklist

• [ ] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation if necessary (this includes comments as well)
• [ ] I have added tests that prove my fix is effective or that my feature works

[achingbrain]

Test to see if it still breaks rust compatibility, not ready for merging.