cli: Improve error handling of toolchain overrides

[acheroncrypto]

Problem

• If solana_version override restoration fails, it fails silently — there is no indication of failure
• [toolchain] override and restoration code is similar but they live in separate functions

Summary of changes

• Show error if toolchain restoration fails
• Failure during one of the toolchain restoration steps no longer fails the entire function
• Set toolchain override and restoration in the same place

[vercel]

@acheroncrypto is attempting to deploy a commit to the coral-xyz Team on Vercel.

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