Consider @ThreadSafe when importing Java types

[ktoso]

While "dormant" some project do use the JSR-305 annotations, and one of them is https://www.javadoc.io/doc/com.google.code.findbugs/jsr305/latest/javax/annotation/concurrent/ThreadSafe.html

This is something we could use to annotate such imported Java types as Sendable.

Others are:

Name	Description
GuardedBy	The field or method to which this annotation is applied can only be accessed when holding a particular lock, which may be a built-in (synchronization) lock, or may be an explicit Lock.
Immutable	The class to which this annotation is applied is immutable.
NotThreadSafe	The class to which this annotation is applied is not thread-safe.
ThreadSafe	The class to which this annotation is applied is thread-safe.

[lhoward]

also see #157