Fixes#9405
`sync_point` API provided with incorrect sync point id might allocate
crazy amount of memory and fail with `std::bad_alloc`.
To fix this, we can check if the encoded sync point has been modified
before decoding. We can achieve this by calculating a checksum before
encoding, appending it to the encoded sync point, and compering it with
a checksum calculated in `db::hints::decode` before decoding.
Closes#14534
* github.com:scylladb/scylladb:
db: hints: add checksum to sync point encoding
db: hints: add the version_size constant
eb6202ef9c