src/oscillators: Shaved another op from render_lut_256; use for all sines.

[dpwe]

speedtest-piano imporves from 3416us to 3258us by moving one bit shift out of loop. Also, use render_lut_256 for plain sine and FM unmodulated sine too, since it's faster.

[github-actions]

🎛️ AMY HW CI (AMYboard bench)

Flashed this PR's AMY (LoadTestChord: 6-voice Juno patch=1, one held note every 2 s) onto the physical AMYboard and measured the smoothed render load as the chord grows — back-to-back with the same sketch built at the PR's merge base, so Δ is this PR's own cost.

✅ PASS — the bench ran the test to completion.

notes held	main @ ed6071f	this PR	Δ
1	1022	1015	-7
2	1183	1177	-6
3	1745	1744	-1
4	1928	1926	-2
5	2567	2560	-7
6	2741	2738	-3

Full chord settled render μs: 2739 (was 2744, Δ -0.2%) (peak 2747, 39 samples)

⬇️ Artifacts: serial log · load trace · report

_{Self-hosted bench (amyboardci). FAIL means only that the test could not run — the load values are informational, with no threshold and no audio compare. See tools/arduino_loadsweep/.}

[bwhitman]

⛓️ tulipcc integration PR opened

This merge was pinned into tulipcc for full-system CI: shorepine/tulipcc#1253

Test it there and merge that PR to move tulipcc onto this AMY.