Support gzip serialization

[95-martin-orion]

For comparison with #3655. Observed benchmark results, running locally:

nested: 7.016707049 s
size: 299304
flattened: 1.278540381 s
size: 20911

[95-martin-orion]

Benchmarks have been migrated to the dev_tools/profiling directory. Further tests suggest that the example described above may be an outlier with regards to gzip-serialized data size of heavily-nested circuits - with more gates and slightly less nesting, data size was comparable with (or better than) JSON-serialization.

[mpharrigan]

xref #3438

[95-martin-orion]

xref #3438

I'm sure I saw this issue at some point, but failed to review it prior to this PR. Would you like me to repackage this into the format discussed there? (i.e. to_json({...}, compress=['json','gzip','no',None]))

[mpharrigan]

Would you like me to repackage this

No, just wanted to make sure there was reference to the other discussion

[mpharrigan]

a minor qualm and a major qualm. What should this function be named?

[mpharrigan]

lgtm. sorry about the delay this must have gotten lost in my inbox

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[google-cla]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
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[95-martin-orion]

Ah, the CLA doesn't like the email address that cf706f4 is associated with. I'll rebase and force-push to appease it.