Loader improvements #768

Job	Run time
Build and package cores	8m 55s
Split off zephyr_main	10s
Split off zephyr_contrib	15s
Split off zephyr_unoq	15s
Split off zephyr	14s
Test zephyr_main:giga	2m 31s
Test zephyr_main:portentac33	2m 31s
Test zephyr_main:niclasense	2m 34s
Test zephyr:unoq	2m 26s
Test zephyr_main:nano33ble	2m 34s
Test zephyr_contrib:frdm_mcxn947	2m 20s
Test zephyr_contrib:ek_ra8d1	2m 29s
Test zephyr_contrib:frdm_rw612	2m 35s
Test zephyr_main:portentah7	2m 33s
Test zephyr_main:opta	2m 20s
Collect logs	6s
Publish jsons	15s
verify-core	0s
Publish core	0s
cleanup-artifacts	5s
	35m 8s

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