feat: Implement SQL support in test proxy

[jackdingilian]

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Fixes #<issue_number_goes_here> 🦕

[daniel-sanche]

The changes mostly LGTM, but do you know why the tests are now failing? Is it because of the updated protos?

[daniel-sanche]

I think this should be outside of the handlers folder, and maybe renamed to something like sql_encoding_helpers.py

Or if putting it in a parent folder is tricky, you can make a handlers/helpers folder and put it in there

[jackdingilian]

Done

[daniel-sanche]

@jackdingilian Maybe for this PR we should just ignore the proto updates? Right now our conformance tests are locked on to tag v0.0.2, which doesn't use any btsql functionality. Updating to the latest version of the conformance tests will require a few new library features, and likely won't be prioritized until closer to the end of the year

Maybe for this PR, we should just focus on getting execute_query into the test_proxy so it's ready, and then we'll re-generate the protos in the future when we bump up the conformance test tag?

Let me know what you think

[daniel-sanche]

LGTM

We will have to update the test tag for the sql tests to run, but that can come as a follow up