Add safe LOCAL INFILE support

[iagocavalcante]

Summary

• add an explicit per-query :local_infile file path for text queries
• advertise CLIENT_LOCAL_FILES and decode the 0xFB filename as an EOF string
• stream only the caller-selected file in protocol-sized packets
• keep connections synchronized when the source is missing, invalid, or cannot be read

Security

A MySQL server can request a different client-side path from the one named in the SQL statement. To avoid arbitrary file disclosure, this implementation ignores the server-provided filename and requires callers to pass an explicit path for each query:

MyXQL.query(conn, sql, [],
  query_type: :text,
  local_infile: "/path/to/data.csv"
)

This supersedes #204 and follows the safe, explicit-source direction discussed in #110.

Testing

• mix compile --warnings-as-errors
• mix test --exclude requires_otp_19 against MySQL 8.4
• 215 tests, 0 failures, 2 skipped (8 excluded by environment/tag configuration)

Closes #203