dynamic_module: add new streamable HTTP callout support

[agrawroh]

Description

The Async streamable HTTP client is supported by Envoy since long time. Using it, we can create multiple different HTTP streams to different backends at the same time and distribute requests between these backends.

This PR exposes this feature to dynamic modules. It could be used for developing MCP related dynamic modules.

Fix #42045

---

Commit Message: dynamic_module: add new streamable HTTP callout support
Additional Description: Add support for the Async streamable HTTP client in Dynamic Modules.
Risk Level: Low
Testing: Added Unit + Integration Tests
Docs Changes: Added
Release Notes: Added

[repokitteh-read-only]

As a reminder, PRs marked as draft will not be automatically assigned reviewers,
or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

🐱

Caused by: #42225 was opened by agrawroh.

see: more, trace.

[wbpcode]

Thanks so much for picking this up. One comment to the ABI to start the review. :)

[repokitteh-read-only]

CC @envoyproxy/coverage-shephards: FYI only for changes made to (test/coverage.yaml).
envoyproxy/coverage-shephards assignee is @RyanTheOptimist

🐱

Caused by: #42225 was synchronize by agrawroh.

see: more, trace.

[mathetake]

This is so cool, thank you so much for taking this up! I am trying to think about the way to remove the necessity for "unsafe" on these pointer passing methods but yeah i think there's no way around it seems..

[wbpcode]

Thanks so much for this great contribution. The new ABI lgtm to me. And some comments to the implementation code. :)

/wait

[RyanTheOptimist]

Could we add additional tests to increase coverage?

[agrawroh]

Sorry, I tried my best but there are a few likes I couldn't cover.
Mostly the edge scenarios like stream not ending correctly.

I can open a follow up PR to improve the coverage by adding tests for existing uncovered lines. Hopefully that will be good enough to remove the exception.

[RyanTheOptimist]

Sounds good. Thanks!

[mathetake]

Thank you so much for working on this. LGTM. can we add more tests to avoid having coverage exception?

[agrawroh]

Thank you so much for working on this. LGTM. can we add more tests to avoid having coverage exception?

Thanks! I tried my best but there are a few likes I couldn't cover.
Mostly the edge scenarios like stream not ending correctly.

I can open a follow up PR to improve the coverage by adding tests for existing uncovered lines. Hopefully that will be good enough to remove the exception.