Change default cache dir to user cache dir

[agostbiro]

Problem

The default cache directory is currently relative to the current directory. This clutters the user's machine and it leads to fewer cache hits.

Solution

Use a single cache directory by default for each user, e.g. on Linux

/home/alice/.cache/org.nomic.edr

and on MacOs

/Users/Alice/Library/Caches/org.nomic.edr

This crate can be used to get the base directories.

Definition of done

The cache directory defaults to a single cache directory for each user in the EDR CLI and the cache dir is configured when calling from Hardhat. The library crates should require a cache directory to be passed to them.