The various require() and check() methods in test_utils.hh were
introduced to replace BOOST_REQUIRE() and BOOST_CHECK() respectively in
multi-shard concurrent tests, specifically those in
tests/boost/multishard_mutation_query_test.cc.
This was done literally, just replacing BOOST_REQUIRE() with require()
and BOOST_CHECK() with check(). The problem is that check() is missing a
feature BOOST_CHECK() had: while BOOST_CHECK() doesn't cause an
immediate test failure, just logging an error if the condition fails, it
remembers this failure and will fail the test in the end. check() did
not have this feature and this caused potential errors to just be logged
while the test could still pass fine, causing false-positive tests
passes. This patch fixes this by returning a [[nodiscard]] bool from the
check() methods. The caller can & these together over all calls to
check() methods and manually fail the test in the end. We choose this
method over a hidden global (like BOOST_CHECK() does) for simplicity
sake.
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
