[meta] Interop and local flag days

[rnewman]

There are a number of changes to Mentat's storage schema and capabilities that are an 'event horizon' for syncing: older clients would be unable to sync across it.

We will be addressing this via built-in schema versioning, but it's prudent to track work that would trigger this.

• More datatypes ([meta] Full Datalog type support (instants, UUIDs, URIs) #201): big integers ([core] Implement BigInteger support in TypedValue #280), JSON ([meta] Support a JSON value type #31), non-ns keywords ([tx] Expand TypedValue to include non-namespaced keywords #285), URIs ([meta] Support URIs #431)
• Directory-based and alternate file format (Internal storage schema migration #97, Consider alternative disk representations to minimize database fragmentation #129, Consider a directory-based file format, rather than a single SQLite file #541)
• Alternate datom flag format (Consider an alternative disk representation for datom flags #29)
• More schema alteration support and simpler transacts for schema changes (Further attribute alteration #105, [tx] Handling retracting schema characteristics, like :db/cardinality and :db/unique. #379, Evaluate new Datomic changes #121)
• Excision (Implement excision #21)
• :db/noHistory (Implement :db/noHistory #102)
• Hash-based indexing (Implement a hash-based indexing option for attributes #69)
• Tabular representations (Future: support for hardening parts of a schema into a tabular representation #33)