all: fix test flakiness and improve test infrastructure

Buffer the AuthRequest verdict channel to prevent a race where the
sender blocks indefinitely if the receiver has already timed out, and
increase the auth followup test timeout from 100ms to 5s to prevent
spurious failures under load.

Skip postgres-backed tests when the postgres server is unavailable
instead of calling t.Fatal, which was preventing the rest of the test
suite from running.

Add TestMain to db, types, and policy/v2 packages to chdir to the
source directory before running tests. This ensures relative testdata/
paths resolve correctly when the test binary is executed from an
arbitrary working directory (e.g., via "go tool stress").

hscontrol/db/suite_test.go

@@ -56,7 +56,7 @@ func newPostgresDBForTest(t *testing.T) *url.URL {
 
 	srv, err := postgrestest.Start(ctx)
 	if err != nil {
-		t.Fatal(err)
+		t.Skipf("start postgres: %s", err)
 	}
 
 	t.Cleanup(srv.Cleanup)