turbo: nRF52 boards loader enable native .mpy default

[mikeysklar]

What

Enables the turbo loader (CIRCUITPY_LOAD_NATIVE) by default on nRF52.

38 of 54 boards fit. The other 16 opt out in mpconfigboard.mk. All 16 keep CIRCUITPY on internal flash.

Follow-up to #11332 (RP2), #11355 (STM32F4) and #11356 (SAMx5x).

Hardware tested

Feather nRF52840 Express

10.3.0-66-g55984e753c, which includes this commit.

Board	vsum bytecode	vsum viper .mpy	pixels viper .mpy	pixels @native .mpy
Feather nRF52840 Express	352.1 ms	18.5 ms	841 ms	7,268 ms

How I tested it

All 54 nRF52 boards built in their tightest CI language with GCC 15.2.1.

Hardware used vsum.py from #11332 plus pixels.py.

Tightest boards with the loader	Language	Flash free with the loader
pca10100	ru	148 B
ikigaisense_vita	ja	2,488 B
warmbit_bluepixel	ja	2,520 B
sparkfun_nrf52840_mini	ja	3,112 B
simmel	ru	17,932 B
other 33 boards		27 to 246 KB

Opt-outs	Language	Over by with the loader
bluemicro833	ru	24 B
raytac_mdbt50q-rx	ja	624 B
ADM_B_NRF52840_1	ja	896 B
electronut_labs_papyr	ja	976 B
ssci_isp1807_dev_board	ja	992 B
pca10059	ja	1,080 B
ssci_isp1807_micro_board	ja	1,120 B
raytac_mdbt50q-db-40	ja	1,328 B
teknikio_bluebird	ja	1,344 B
makerdiary_nrf52840_mdk_usb_dongle	ja	1,368 B
nice_nano	ja	1,568 B
pillbug	ja	1,584 B
supermini_nrf52840	ja	1,616 B
bless_dev_board_multi_sensor	ja	1,680 B
electronut_labs_blip	ja	1,744 B
bluemicro840	ja	1,856 B

Scope

Xtensa and nRF54 (zephyr-cp) loader support will be separate PRs.

AI assistance

Claude Code was used.