Find all conflicts in one round

[penguin-wwy]

Changes:

• Find all dependency conflicts in one round by caching all NoCandidateFound until the end of the round

Contributor checklist

• Provided the tests for the changes.
• Assure PR title is short, clear, and good to be included in the user-oriented changelog

Maintainer checklist

• Assure one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[atugushev]

The legacy resolver is deprecated and will be removed later. Which is why we accept only bug fixes. Thanks for the PR anyway!