flaky: TestSimpleRNN_LossDecreases fails on a docs-only PR, passes on re-run #1010

TestSimpleRNN_LossDecreases in layers/recurrent failed once on a docs-only PR and passed on re-run at the same commit.

• PR docs(distribution): replace the withdrawn 241 tok/s figure with the recorded 235 tok/s run #1007, head be02b20 (four files under docs/distribution, no Go changes).
• Run 35364501929, job test (1.26), step Unit tests: --- FAIL: TestSimpleRNN_LossDecreases (0.00s) then FAIL github.com/zerfoo/zerfoo/layers/recurrent 0.017s.
• Re-run of the failed job at the same head: pass. main at 00616d8 (ci run 35364457627) also passed the same job an hour earlier.

A 0.00s test that asserts a loss decreases is sensitive to its initial weights or to a random seed. Worth pinning the seed or asserting over more steps so the gate stops flaking on unrelated PRs. Opened by chief-planner while gating #1007.