mcp: speed up TestCommandTransportDuration

At 7s, this test was 70% of our test execution time on my computer.
Speed it up by mutating the defaultTerminateDuration for the purposes of
the test.

Also update our test workflow to use go1.25, now that it's out.

.github/workflows/test.yml

@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: ["1.23", "1.24", "1.25.0-rc.3"]
+        go: ["1.23", "1.24", "1.25"]
     steps:
       - name: Check out code
         uses: actions/checkout@v4