zephyr-cp: boot_out.txt reports a stale version on incremental builds #10

Cosmetic but misleading. After an incremental rebuild, a freshly flashed image reported:

Adafruit CircuitPython 10.3.0-alpha.4-71-gb4709a238c on 2026-09-05; Raspberry Pi Pico with rp2040
Board ID:raspberrypi_rpi_pico_w_zephyr

b4709a238c is the base commit and 2026-09-05 an earlier session's date, yet that image demonstrably contained work committed days later — verified by symbol inspection of the flashed ELF (348 bleio symbols and the CYW43 HCI driver, none of which exist at the base commit, plus CONFIG_BT_CYW43_SHARED_BUS=y).

So the version header is not regenerated when only some of the build is stale. The firmware is correct; its self-reported identity is not, which would mislead anyone diagnosing a board from its version string or a bug report. A clean build presumably gets it right.