libflux: refactor reactor/watcher implementation #2465

Job	Run time
spelling	6s
validate commits	0s
Generate build matrix	7s
python linting	28s
bookworm - test-install	12m 9s
bookworm - 32 bit	13m 12s
noble - test-install	13m 13s
el9 - test-install	12m 15s
alpine - test-install	12m 35s
fedora40 - test-install	11m 51s
jammy - test-install	12m 17s
focal - py3.8	16m 39s
bookworm - gcc-12,content-s3,distcheck	19m 31s
fedora40 - clang-18	17m 28s
coverage	24m 24s
el8 - ascii	19m 46s
el8 - test-install	13m 50s
el8 - system,coverage	7m 37s
inception	21m 31s
flux-pmix check	12m 58s
flux-pam check	4m 17s
flux-accounting check	4m 38s
flux-sched check	6m 53s
Generate docker manifest	1s
	4h 17m 46s

Provide feedback