fallback behavior on version set failure

[hendriknielaender]

In the case of a failure when setting a new Zig version, it would be more user-friendly for ZVM to automatically fallback to the last successfully installed and set Zig version. This fallback mechanism would ensure that the user's environment remains in a usable state, allowing them to continue working with the last known good configuration until they decide to address the issue that caused the version set operation to fail.

Steps to Reproduce

1. Ensure ZVM is installed and a Zig version is currently set and being used.
2. Attempt to set a new Zig version using ZVM to one that is invalid or will cause the set operation to fail (e.g., due to a typo in the version name or a temporary network issue).
3. Observe that after the failure, the Zig version is unset, and commands relying on Zig will not work until the user manually intervenes.

Possible Solution

Implement a feature in ZVM where, upon a failed attempt to set a new Zig version, it automatically reverts to the most recently used version that was successfully installed and set. This could involve keeping a history of used versions and ensuring there's a quick way to revert to the previous state without user intervention.

[hendriknielaender]

https://github.com/hendriknielaender/zvm/pull/34/files