issue: Implement doorbell batching for the new API

[pasis]

Description

New API requires user to call explicit flush. We can implement doorbell batching and close unfinished batch by the flush. This will guarantee doorbell and zcopy completions progress even if user stops sending data.

What

Implement doorbell batching for the new API.

Why ?

Up to 4% performance improvement depending on scenario.

Change type

What kind of change does this PR introduce?

• [ ] Bugfix
• [x] Feature
• [ ] Code style update
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [ ] Tests
• [ ] Other

Check list

• [ ] Code follows the style de facto guidelines of this project
• [ ] Comments have been inserted in hard to understand places
• [ ] Documentation has been updated (if necessary)
• [ ] Test has been added (if possible)

[galnoam]

bot:retest

[galnoam]

Hi @pasis, what is the status? If its in progress draft, lets keep it in the private fork.