http-service-hyper: Make serve return a Future

[tirr-c]

Description

• Renamed the original serve to run.
• Added the new serve which returns a Future that can be awaited on.

Motivation and Context

Using the new serve, server Future can be run concurrently with other Futures easily.

How Has This Been Tested?

I've briefly tested serve with Tide and Runtime Tokio and it worked.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[yoshuawuyts]

@tirr-c I'm thinking, perhaps if we rename serve to run, and serve_async to serve, it might create a bit clearer distinction between the purpose of each method -- similar to Hyper's naming scheme.

[tirr-c]

@yoshuawuyts Changed function names, and this is a breaking change. I've updated the PR description accordingly.

[yoshuawuyts]

Looks great!