Add fields tests, and rename XYZParams to XYZConfig for fields

[Pratyush]

Description

Fix test generation for Fq12, and also complete renaming of field XYZParams to XYZConfig.

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (master)
• Linked to GitHub issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
• Updated relevant documentation in the code
• Added a relevant changelog entry to the Pending section in CHANGELOG.md
• Re-reviewed Files changed in the GitHub PR explorer

[weikengchen]

Let me add an entry in the CHANGELOG about the renaming of XYZParams to XYZConfig, which I believe is a breaking change.

[weikengchen]

Pratyush: please see if the CHANGELOG entry is okay, and you may want to change the title of this PR, and then we can merge it.