feat(self-update): show old version in update message

[mkniewallner]

Summary

Indicate the previous version from which uv was upgraded when running uv self update. Thought that it could be useful in some situations to have a trace of the previous version that was installed.

Test Plan

Did not find a way to test this, since this heavily relies on being able to use the installation script and the ability to publish artifacts for a specific tag.

[zanieb]

Ah this sounds quite nice.

[notatallshaw]

This fixed https://github.com/astral-sh/uv/issues/4748 right?

[zanieb]

Thank you!