refactor: change custom protocol handler input to an owned Request

[lucasfernog]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

Checklist

• This PR will resolve #___
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary
• It can be built on all targets and pass CI/CD.

Other information

[wusyong]

Can we take this chance to refactor to Request<Cow<'static, [u8]>>?
This could reduce some vector allocations.

[lucasfernog]

@wusyong I couldn't really see the improvement, the request body will never be an static [u8].

[wusyong]

Or could it be Cow<'_, [u8]>? Because I know many of original types can be deref to u8 slice.

[amrbashir]

Closing since this change has been merged in #1017