Fix AS::Cache 7.1 format to properly compress bare strings

[casperisfine]

The bare string and compression features weren't working properly together.

I discovered this while trying to fix deprecation warnings.

FYI: @jonathanhefner

[jonathanhefner]

Thank you for fixing this! ❤️

Something to note: this will prefix bare strings with MARK_UNCOMPRESSED or MARK_COMPRESSED when using the 7.1 coder. My original intent was to dump bare strings independently of the coder, using their own dedicated prefixes. Obviously, I messed that up with Marshal71WithFallback#dump_compressed, but that is how it works with the MessagePackWithFallback coder.

This is also fixed in #48451 since bare strings are actually dumped independently of the coder (aka serializer). #48451 offloads this logic to SerializerAdapter so that the serializer is only concerned with serialization and versioning, and the compressor is only concerned with compression and versioning. For example, see Marshal71WithFallback in #48451

[byroot]

Something to note: this will prefix bare strings with MARK_UNCOMPRESSED or MARK_COMPRESSED when using the 7.1 coder.

Yes, it's not ideal. As mentioned in #48451 the prefix, expires_at and even version shouldn't be compressed, only the payload should.

I really need to wrap my head around #48451 -_-