ci(v3): improve usage of github actions cache

[galargh]

• Because this PR includes a bug fix, relevant tests have been included.
• Because this PR includes a new feature, the change was previously discussed on an Issue or with someone from the team.
• I didn't do anything of this.

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This PR is a subset of #5301 and, unlike the original, it targets the v-next branch.

In this PR, I split the population of the GitHub Actions cache from its' usage. I do this by adding a new workflow responsible only for generating new GitHub Actions cache entries on changes to the pnpm lockfiles and updating all the other workflows to only read from the cache rather than reading and writing to it. Additionally, I create a helper action which abstracts away environment setup (installation of node, pnpm and cache setup).

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Name	Status	Preview	Comments	Updated (UTC)
hardhat	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 2, 2024 3:03pm

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