v0.16.0-next.0

• We now throw an error if any primary key columns are set to be nullable.
  • Null primary keys are not allowed in any DB except SQLite.
  • SQLite doesn't enforce uniqueness when a primary key is set to null. I.e., you can have many duplicate rows with a null value in the primary key column.
  • This latter problem completely breaks any attempts at merging
• ✅ 10x improvement in perf when migrating crr tables
• ❌ 15% reduction in perf when writing to crr tables :(
• ✅ 5x reduction in CRDT metadata (at the cost of the above write perf)
• Compilable under libsql
• site id is now a required column in crsql_changes
• release artifacts are zip files containing the properly named loadable extension. This removes the need for a rename step #385