[Feature] Nested executor #1920

Job	Run time
black	12s
uv_check	11s
mypy	10s
minimal	5m 48s
benchmark (ubuntu-latest, 3.14, .ci_support/environment-openmpi.yml)	7m 28s
notebooks_integration	17m 53s
pip_check	39s
benchmark (ubuntu-latest, 3.14, .ci_support/environment-mpich.yml)	6m 56s
notebooks	1m 30s
unittest_flux_mpich	5m 51s
unittest_old	5m 47s
unittest_win	7m 31s
unittest_openmpi (ubuntu-latest, 3.12)	5m 47s
unittest_slurm_mpich	3m 9s
unittest_openmpi (ubuntu-24.04-arm, 3.14)	5m 45s
unittest_openmpi (ubuntu-latest, 3.14)	5m 47s
unittest_openmpi (ubuntu-22.04-arm, 3.14)	5m 48s
unittest_openmpi (macos-latest, 3.14)	5m 57s
unittest_openmpi (ubuntu-latest, 3.13)	5m 49s
unittest_openmpi (ubuntu-latest, 3.11)	5m 50s
unittest_flux_openmpi	5m 56s
unittest_mpich (ubuntu-22.04-arm, 3.14)	5m 48s
unittest_mpich (ubuntu-latest, 3.11)	4m 41s
unittest_mpich (macos-latest, 3.14)	6m 5s
unittest_mpich (ubuntu-latest, 3.14)	2m 12s
unittest_mpich (ubuntu-latest, 3.12)	3m 44s
unittest_mpich (ubuntu-24.04-arm, 3.14)	5m 47s
unittest_mpich (ubuntu-latest, 3.13)	1m 45s
black_fix	0s
autobot	-1s
uml	-1s
	2h 19m 44s

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