fix: harden Arrow JSON ingest (#452)

[cofin]

Fixes #452.

Summary:

• register asyncpg json/jsonb codecs in binary mode, including JSONB version-byte handling
• align cockroach_asyncpg connection init with asyncpg JSON codec registration
• prepare nested Arrow rows for SQLite/MySQL-family bridged loaders and cache Arrow schema prep decisions
• tighten psqlpy JSON fallback and Spanner Arrow parameter-type caching
• add Oracle, DuckDB, psycopg, psqlpy, asyncpg, Cockroach, SQLite, MySQL-family, and Spanner regression coverage