Add support for capturing RTS statistics from compilation

This adds a simple mechanism for capture runtime system statistics from compiler invocations. It's pretty crude, but should nevertheless be useful.

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• c3ba61ec - Use cabal v2-* commands instead of new-*
• e7e5c5cf - ci: Set --store-dir explicitly

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• 135ed46e - Add perf support

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• 5cdd1a70 - run-ci: document it

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• 7f5e11e0 - run-ci: Briefly describe configuration file intent

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• c9fe6fad - Disable perf counters for now

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