Data races

I tried adding the `-race` flag to the `make test` target and four tests began to fail. We should track down the root causes of the data races in these tests and fix them:

- [ ] `TestAuthorization` in `pkg/http`
- [ ] `TestProviderWatchTargetsTestSuite` in `pkg/kubernetes`
- [ ] `TestSIGHUP` in `pkg/kubernetes-mcp-server/cmd`
- [ ] `TestWatchClusterState` in `pkg/mcp`