gitrest: Compress latest summary with Pako deflate

[znewton]

Description

Isomorphic-Git automatically compresses everything written to storage using pako.deflate. However, when we added the "latestFullSummary" blob optimization, we did not compress it. From a local test, for simple summaries compression would reduce size by 80%.

Old summaries will not be "inflatable", so the error from attempting to inflate them is handled. This is ideal, IMO, compared to implementing our own header check in place of relying on Pako's.

This PR should be used in conjunction with #19285 because we have so-far been dependent on the "latestFullSummary" blob to check if the decompressed summary size is too large. Instead, we will have to start depending on blocking too large writes.