fix: HttpOpen post request data

[zees-dev]

Context

A caller cannot provide post request data since there is no helper function for the HttpOptions; neither are the struct attributes publicly exported.

Fixes

This PR simply:

• makes the HttpOptions variables public
• fixes a typo in the same file
• applies cargo fmt --all to all files (no code changes)
• sets default-features = false for the only json dependency; to explicitly reduce compiled code/binary size

[dmikey]

lg2m