Replace Tesla with Req

[joshprice]

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Is your feature request related to a problem? Please describe.

We typically use Req across the Ash ecosystem rather than Tesla, so we want to align on a single HTTP client library.

Describe the solution you'd like

As discussed in Ash Office Hours, Req now supports pipelines like Tesla does and this could be a decent upgrade.

Describe alternatives you've considered

No response

Additional context

No response