fix: Allocate HTTP header space for async httpd_req_t objects (IDFGH-12445)

[tmiw]

This resolves bug #13430 by allocating a new copy of resp_hdrs when calling httpd_req_async_handler_begin(), thus preventing invalid access to memory from async tasks.

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[mahavirj]

Some minor comments, otherwise LGTM!

[tmiw]

Some minor comments, otherwise LGTM!

Thanks for the feedback! I just pushed some changes to address the formatting/naming comments you had. Let me know if you end up seeing anything else.

[mahavirj]

@tmiw Can you please squash the commits?

[tmiw]

@tmiw Can you please squash the commits?

Done.

[mahavirj]

sha=f799e9990952847be9d91b2051356fc8f2879676