release 5.2.0

fix(package): include modules in package `__all__`

feat(process/pool): abort all tasks on BrokenProcessPool error

fix(pool/process): handle pickling errors on the channel's receiver

feat(pool): add logic to abort all ongoing tasks

fix(pool/process): removed unused import

test(pool): add unpicklable returned value tests

chore(doc): update copyright year

chore: update copyright year

fix(test): avoid leaking resources in corner case tests

fix(process): cleanup process resources upon SIGTERM requests

fix(common): add process exiting routine

fix(process): do not pass unnecessary resources to child process

fix(pool): ensure all resources are lazily created

fix(tests): pass the proper context to the pool