1871 thread-safety for the cache-based datasets

[wyli]

Fixes #1871

Description

this PR addresses cache-based dataset multi-thread preloading issues by:

• adding a monai.transforms.ThreadUnsafe API, the unsafe transforms will be deepcopied in the cache computation.
• revise all transforms to be either thread-safe or inheriting ThreadUnsafe
• updated persistent dataset although it's not using multi-threading, mainly to keep the behaviour consistent with the cache-based ones

all the randomisables are not thread-safe, but we only use them with multi-process dataloader, there's no multi-thread issue.

Status

Ready

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[wyli]

/black
/integration-test
/black

[Nic-Ma]

Thanks for the enhancement for CacheDataset, it's heavily used in NVIDIA Clara project, I will try to review this PR as soon as possible.

[Nic-Ma]

Thanks for the enhancement, put several comments inline.
Others look good to me.

Thanks.