cleanup: rename Equals to Equal

tl;dr `s/Equals(/Equal(/g`

Much of Nomad's code predates Go convention, including our `Equals` methods. It seems `Equal` (no s) is becoming the norm.

e.g. https://pkg.go.dev/golang.org/x/exp/maps#Equal

Let's update Nomad to follow the convention.

Search the repository for Equals method declarations and calls, then review the affected Go packages to confirm the rename is consistent. Update every occurrence to Equal and run the affected Go tests; done means no intended Equals methods or calls remain and the tests pass.

Written by the indexing model from the issue text.