Resolve traitlets type warnings, lint, remove `six` #1631

Job	Run time
build (ubuntu, >=16,<17.0.0a0, >=4.0.0,<5.0.0a0, >=4)	3m 22s
build (ubuntu, >=16,<17.0.0a0, >=4.0.0,<5.0.0a0, >=4)	3m 22s
jstest/lint (ubuntu, >=16,<17.0.0a0, >=4.0.6,<5.0.0a0, >=4)	5m 25s
jstest/lint (ubuntu, >=16,<17.0.0a0, >=4.0.6,<5.0.0a0, >=4)	5m 25s
smoke source install ubuntu py3.8 lab>=4,<5	1m 38s
smoke source install ubuntu py3.8 lab>=4,<5	1m 38s
atest ubuntu py3.8 r>=4	3m 48s
atest ubuntu py3.8 r>=4	3m 52s
smoke source install ubuntu py3.11 lab>=4,<5	1m 37s
smoke source install ubuntu py3.11 lab>=4,<5	1m 37s
atest ubuntu py3.11 r>=4	3m 47s
atest ubuntu py3.11 r>=4	3m 47s
atest macos py3.8 r>=4	7m 47s
atest macos py3.8 r>=4	7m 47s
atest macos py3.11 r>=4	9m 23s
atest macos py3.11 r>=4	9m 23s
atest windows py3.8 r>=4	10m 48s
atest windows py3.8 r>=4	10m 48s
atest windows py3.11 r>=4	13m 50s
atest windows py3.11 r>=4	13m 50s
smoke ubuntu py3.8	32s
smoke ubuntu py3.8	32s
smoke ubuntu py3.11	40s
smoke ubuntu py3.11	40s
smoke ubuntu pypypy-3.8	1m 27s
smoke ubuntu pypypy-3.8	1m 27s
smoke macos py3.8	1m 4s
smoke macos py3.8	1m 4s
smoke macos py3.11	1m 15s
smoke macos py3.11	1m 15s
smoke macos pypypy-3.8	1m 3s
smoke macos pypypy-3.8	1m 3s
smoke windows py3.8	1m 34s
smoke windows py3.8	1m 34s
smoke windows py3.11	1m 44s
smoke windows py3.11	1m 44s
smoke windows pypypy-3.8	5m 30s
smoke windows pypypy-3.8	5m 30s
	2h 32m 32s

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