Install boost from package manager, not source

[PhilMiller]

This'll make the pipelines somewhat less flaky, since they won't rely on an unsupported download source.

It'll also exercise a broader range of versions of Boost than the fixed 1.72 that we were previously testing.

Changes

• In Github CI jobs that don't build a Docker image, get Boost from apt on Ubuntu and brew on macOS

Testing

1. Impacts only CI pipelines

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

Target Environment support

• Linux
• macOS

[PhilMiller]

This is mostly a test to see whether we can stop grabbing boost source tarballs and just use the packaged versions available.

This does make us vulnerable to version skew leaving us with incompatibility. I'll see if there's a different Boost mirror that's more cooperative.

[PhilMiller]

Maybe let's not do this - see #700