Reject ignored statements and run all of them in executemultiple - #364

Closes #303.

SQL with several statements silently ran only the first one:

julia> DBInterface.execute(db, "CREATE TABLE m(a); INSERT INTO m VALUES (1)");

julia> DBInterface.execute(db, "SELECT count(*) FROM m") |> columntable
(var"count(*)" = [0],)     # the INSERT never ran, and nothing said so

julia> DBInterface.executemultiple(db, "SELECT 1 AS a; SELECT 2 AS b") |> collect
1-element ...              # only the first result

sqlite3_prepare_v2 reports where the first statement ends; we passed C_NULL for that and dropped the rest.

• DBInterface.prepare, DBInterface.execute, and SQLite.execute now throw ArgumentError if anything but whitespace or comments follows the first statement. Python's sqlite3 does the same. Trailing ;, whitespace, and comments still work.
• DBInterface.executemultiple(db, sql, [params]) runs every statement in order and returns their cursors. Each statement is prepared only after the previous one runs, so CREATE TABLE ...; INSERT INTO ... works. The same params go to every statement, so named parameters work across statements.

Behavior change: code that passed several statements to execute used to run only the first. It now errors, pointing to executemultiple. I think that's the right call, since the old behavior silently dropped writes, but it's worth a minor version bump.

🤖 Generated with Claude Code