FetchContent requires CMake 3.11 (released Mar 28, 2018).
Fixed this warning:
```
CMake Warning (dev) at /usr/share/cmake/Modules/FetchContent.cmake:1316 (message):
The DOWNLOAD_EXTRACT_TIMESTAMP option was not given and policy CMP0135 is
not set. The policy's OLD behavior will be used. When using a URL
download, the timestamps of extracted files should preferably be that of
the time of extraction, otherwise code that depends on the extracted
contents might not be rebuilt if the URL changes. The OLD behavior
preserves the timestamps from the archive instead, but this is usually not
what you want. Update your project to the NEW behavior or specify the
DOWNLOAD_EXTRACT_TIMESTAMP option with a value of true to avoid this
robustness issue.
Call Stack (most recent call first):
imgui/CMakeLists.txt:23 (FetchContent_Declare)
```
Previously this was unlimited, which could result in holding on to a
large amount of memory if the connection got backlogged or a burst of
data transmission occurred.
The following source code changes were required:
* Whitespace changes from spotless
* PMD warning suppressions for utility class tests
* PMD warning rename from "BeanMembersShouldSerialize" to
"NonSerializableClass"
* Declared more class members as final
This works around an exit race with wpi::Now() on Rio; it was overridden
to call HAL_GetFPGATime(), which calls chipobject, but on exit, because
there was not a library dependency, the chipobject could be destroyed
prior to wpiutil/wpinet being shut down.
The algorithm being used for scanning outgoing messages was O(n^2)
because it did a full linear search and then appended. This scan is
performed for each client. If there is a burst of outgoing changes, the
outgoing queue can get quite deep all at once and this scan can be very
slow. Replacing with a map fixes this.
There's a spec difference between NT4 and datalog for integers; NT4 uses
"int", datalog uses "int64". We were using "int" for datalog as well.
Also add backwards compatibility support to datalogtool for treating
"int" as "int64".
Previously the timeout was 10 times the update rate, so with low update
rates it could be as small as 50 ms, causing spurious disconnects when
large or many topics were published.
Previously, a setDefault() on the server could override a client doing a
real set() if the time offset between client and server was negative,
resulting in a negative timestamp from the client. This is a not
uncommon situation with robot code, as the robot code always starts at
time 0, so any clients that set values earlier (in real time) would have
negative timestamps.
Also improve special casing of 0 in the transmit side to make sure a
normal timestamp will never get sent as 0.
Previously this wouldn't send the last value on the value subscribe if a
topics only subscription already existed.
Also start adding server implementation unit tests.
This avoids the warning appearing on every startup when persistent
values aren't used.
Also add note to message saying it can be ignored if persistent values
aren't expected.
