Fix typos in comments, tests and function names

[alexandear]

Golang code usually used marshal instead of marshall.

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[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

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What to do if you already signed the CLA

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• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
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[alexandear]

@googlebot I signed it!

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CLAs look good, thanks!

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[dsnet]

Thank you

[tandr]

https://en.wikipedia.org/wiki/Marshalling_(computer_science)
https://en.wikipedia.org/wiki/Marshalling (double L) seems to be a correct spelling of the term, sorry.

[alexandear]

@tandr https://github.com/golang/go/wiki/Spelling