POC: Add storage to cache policy

[desertaxle]

Potential DX for specifying where to store cache entries.

Example:

from prefect import task
from prefect.cache_policies import Inputs
from prefect.transactions import IsolationLevel


@task(
    cache_policy=Inputs(
        storage="~/.prefect/cache",
        locks="~/.prefect/locks",
        isolation_level=IsolationLevel.SERIALIZABLE,
    )
)
def my_task(x):
    return x


if __name__ == "__main__":
    print(my_task(10))

This task will store result metadata as a cache/transaction record at ~/.prefect/cache and the raw result to ~/.prefect/storage.

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

[codspeed-hq]

CodSpeed Performance Report

Merging #15368 will not alter performance

_{Comparing cache-policy-storage (f2c768c) with main (164d52e)}

Summary

✅ 3 untouched benchmarks

[desertaxle]

Closing in favor of #15382