What's the problem this feature will solve?

Pip currently caches built wheels. In several circumstances pip needs to prepare metadata that will not lead to build a wheel (such as during dependency resolution when several versions need to be considered).

Since metadata preparation can be a costly process in itself, a cache of prepared metadata may help resolution performance.

Describe the solution you'd like

A new metadata cache that would work in a very similar way as the wheel cache (same keys, same criteria for deciding whether to cache or not. Feasibility and implementation details to be investigated.

Alternative Solutions

None.

Additional context

#11126 (comment)

Code of Conduct

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