Introduce purs-tidy formatter

[thomashoneyman]

Description of the change
Introduces the purs-tidy formatter. This formatter is a lightly opinionated tool we use to maintain a consistent style in the contrib libraries.

We ordinarily restrict to tools provided by the core or contrib projects. This tool is not, but it was developed and is maintained by core team members, and because it's a formatter it can't block maintenance or release of this library even in the event something goes catastrophically wrong with it.

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Checklist:

• Added the change to the changelog's "Unreleased" section with a link to this PR and your username
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation in the README and/or documentation directory
• Added a test for the contribution (if applicable)

[thomashoneyman]

@purescript-contrib/maintainers This is a draft pull request demonstrating introducing the purs-tidy formatter. This has been opened by an automated script, and if it looks good then all we really need to do is evaluate formatting decisions made by purs-tidy to fix up anything particularly wonky before committing.

If the formatting looks fine then please go ahead and approve, and if it doesn't then please comment on the PR with a suggested fix. I'll do the pull requests in batches and will leave each batch open for a few days for review feedback before merging them in.

If you would like to not be assigned or pinged when new batches go up, please let me know and I'll remove you!

[JordanMartinez]

A few comments, but otherwise LGTM.