Upgrade Go to 1.24 (#2282)
* Upgrade go to 1.24.2
* remove toolchain directive
no longer needed in go 1.24+
* port tools to go tools, fixes import issues
* Update CONTRIBUTING.md
* add TODO for moving golangci-lint to a binary install later
* add gotest.tools/gotestsum to tools
* remove tools.go now that it's in go.mod
