This patch adds a test file, test/alternator/test_encoding.py, testing
how Alternator stores its data in the underlying CQL database. We test
how tables are named, and how attributes of different types are encoded
into CQL.
The test, which begins with a long comment, also doubles as developer-
oriented *documention* on how Alternator encodes its data in the CQL
database. This documentation is not intended for end-users - we do
not want to officially support reading or writing Alternator tables
through CQL. But once in a while, this information can come in handy
for developers.
More importantly, this test will also serve as a regression test,
verifying that Alternator's encoding doesn't change unintentionally.
If we make an unintentional change to the way that Alternator stores
its data, this can break upgrades: The new code might not be able to
read or write the old table with its old encoding. So it's important
to make sure we never make such unintentional changes to the encoding
of Alternator's data. If we ever do make *intentional* changes to
Alternator's data encoding, we will need to fix the relevant test;
But also not forget to make sure that the new code is able to read
the old encoding as well.
The new tests use both "dynamodb" (Alternator) and "cql" fixtures,
to test how CQL sees the Alternator tables. So naturally are these
tests are marked "scylla_only" and skipped on DynamoDB.
Fixes#19770.
Closesscylladb/scylladb#28866
