formula: add size information to JSON API

[cho-m]

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Will be using this PR to essentially jot some ideas down. Needs #18172 beforehand. May end up combining parts of this into other PR.

• General idea right now is to let JSON code path pick up already fetched manifests and populate size information if they exist.
• Re-use brew fetch so we can make use of --concurrency with new --only-manifests to pull quickly pull down all formulae manifests.
• Need to find where to inject the information to bypass manifest fetch when loading API data

[MikeMcQuaid]

Needs #18172 beforehand.

For cases like this:

• push branch to Homebrew/brew, not a fork (this is generally favourable for PRs anyway!)
• set the base branch to the cmd/info: show size information #18172 branch
• rebase on cmd/info: show size information #18172

This means the diff/CI will be correct and it'll fall through to targeting master when that PR is merged.

[MikeMcQuaid]

Makes sense! Good to go when ready.

[MikeMcQuaid]

Actually: not seeing where this is added to JSON API yet but assuming that's coming later.

As we discussed before I think it makes sense to:

• have multiple sizes across the variations when they are available
• consider having a top-level size key that is the only size if only one is available and something like the mean size if multiple are?