TUI "closeness" evaluation

[msuozzo]

It would be nice to display an evaluation of how close a failed rebuild is to success from the TUI summary view. The two main cases to support would be build failures and comparison failures. Build failures could use a coarse metric of how many steps were observed to run (tricky with nested commands like npx. might want to split these out and use set -eux) possibly with some log length metric. Comparison failures could be evaluated using ContentSummary for now and could be augmented with richer diffs.

The UI could be a two-segment progress bar (with a fancier structure than below), the first being build success and the second being comparison completeness:

npm foo 1.0.0      [o___|____]
npm bar 1.0.0      [oooo|o___]

Assuming this to be a monotonic indicator of success would have issues: With this approach, you could imagine a local maxima of a build that succeeds but is of a substantially lower complexity than is necessary. Still, it could be a good, quick, indicator of progress, especially if we disaggregate results by verdict (or have many verdicts for a single artifact/package).