Swap httr out for httr2

[sckott]

Description

Removed the http client httr and now are using httr2 throughout the package.

Reason for this is that httr has entered a stage where they're not really working on the package anymore, and shifting focus to httr2. Had to wait a bit to do this until webmockr and vcr supported httr2 (only used in tests, but still important)

Related Issue

fixes #21

Example

run any fxn in the package ...

Testing

• Tests in this package are passing locally and on CI
• Ran the proof shiny app with this package and it works smoothly

[seankross]

Generally looks good to me, two questions above. Thanks for this, looks cool!