feat: Move safe IP address handling code from edx-platform

[timmc-edx]

This will allow using the code in all IDAs.

Part of https://github.com/openedx/edx-django-utils/issues/241. Code will be removed from edx-platform in https://github.com/openedx/edx-platform/pull/31000.

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Commits best reviewed separately.

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Merge checklist:

• [x] Version bumped
• [x] Changelog record added
• [x] Documentation updated (not only docstrings)
• [x] Commits are squashed

[timmc-edx]

I don't like repeating the PR title in the body. I can link in the pending edx-platform PR, though. Do you think there's more that needs to be said beyond that?

[timmc-edx]

I'm going to try to improve coverage and add pragmas where it doesn't seem worth it.

[robrap]

I don't like repeating the PR title in the body. I can link in the pending edx-platform PR, though. Do you think there's more that needs to be said beyond that?

Nope. We just have different preferences. Your PR. Go with yours. 🙂

[timmc-edx]

Rewrote branch into two commits: One that's basically a straight copy, and one that makes new changes.

[timmc-edx]

(rebased onto master)

[timmc-edx]

(adjusted changelog date)