35163c3 introduced a new use of `mask` which makes the server
process uninterruptible while waiting for a new incoming request.
This change fixes that by surrounding the logic that waits for a
new request with `unmask`. This new `unmask` should still
respect the finalization guarantees of the surrounding masked
code.
Previously, grpc-haskell used a lot of code in the form of
```
do x <- acquireResource
f x `finally` releaseResource x
```
This is not safe since you can get killed after acquiring the resource
but before installing the exception handler via `finally`. We have
seen various gRPC assertion errors and crashes on shutdown when this
got triggered.
Note that even though we can now build grpc-haskell and grpc-haskell-core
with modern tasty, the environment in which we built those test programs
did not support actually running all them successfully, due to the need to test
generated code in the context of the appropriate libraries. We do not yet
know whether test programs built with new versions of tasty would succeed
in the appropriate environment. In principle this could be discovered, but
the work involved is far from trivial, and therefore we defer it to another
time. Tests built with the old tasty still succeed.
