Allow hackney 3.x (current constraint blocks upgrades)

[kevsommer]

ex_aws currently only supports/locks hackney around ~> 1.9.

As of the 27th of Jan, 2026 hackney has released version 3.0 with some breaking changes.

Could you merge #1199 and fix any breaking changes required by the major update: https://hexdocs.pm/hackney/news.html#3-0-0-2026-01-27

[acrogenesis]

Here's a PR taking into account the changes on 2.x and 3.x
#1209