Add build/bundle times to echoed output

It would be very nice if I could see how long it took to perform microbundle and it would be even nicer if I could see how long it took to bundle each dist.

Start by locating the code that echoes microbundle's build output and the entry point that processes each dist bundle. Check how build completion is currently reported. Done means the output includes total build time and the time spent bundling each dist, with coverage verified through the relevant existing checks.

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