`struct CdfThreadContext`: convert to Arc #3790

Job	Run time
test-on-macos-latest	5m 28s
test-on-ubuntu-latest (x86_64-unknown-linux-gnu, release, --release --no-default-features --featu...	2m 15s
test-on-ubuntu-latest (x86_64-unknown-linux-gnu, release, --release --no-default-features --featu...	2m 11s
test-on-ubuntu-latest (x86_64-unknown-linux-gnu, release, --release --no-default-features --featu...	1m 47s
test-on-ubuntu-latest (x86_64-unknown-linux-gnu, opt-dev, --profile opt-dev, 2)	3m 4s
test-on-ubuntu-latest (x86_64-unknown-linux-gnu, opt-dev, --profile opt-dev, 2, -f 1)	2m 25s
test-on-ubuntu-latest (x86_64-unknown-linux-gnu, opt-dev, --profile opt-dev, 2, -f 2)	3m 31s
test-on-ubuntu-latest (i686-unknown-linux-gnu, release, --release --no-default-features --feature...	2m 18s
test-on-ubuntu-latest (i686-unknown-linux-gnu, release, --release --no-default-features --feature...	2m 15s
test-on-ubuntu-latest (i686-unknown-linux-gnu, release, --release --no-default-features --feature...	2m 19s
test-on-ubuntu-latest (i686-unknown-linux-gnu, opt-dev, --profile opt-dev, 2)	1m 55s
test-on-ubuntu-latest (i686-unknown-linux-gnu, opt-dev, --profile opt-dev, 2, -f 1)	2m 4s
test-on-ubuntu-latest (i686-unknown-linux-gnu, opt-dev, --profile opt-dev, 2, -f 2)	2m 55s
	34m 27s

Provide feedback