Support `allow-insecure-host` in `uv python`

[zanieb]

Currently, we do not read this setting during Python downloads.

See https://github.com/astral-sh/uv/pull/6983 for some beginning changes. We'll need to change the internal structuring of the settings a bit to support this.

[zanieb]

@charliermarsh are you opposed to this / moving the setting to a global option or can I mark this as help wanted?

[charliermarsh]

@zanieb -- That seems ok to me. Should keyring also be global?

[zanieb]

@charliermarsh Maybe. I don't see an obvious use-case for it but the network settings make sense for anything that's going to perform requests. Maybe we should move all the network options into a dedicated struct / section?

[charliermarsh]

@zanieb -- Yeah I support that! (Dedicated struct etc.)