fix(sqlite): don't execute a second smuggled-in statement during column inference

[ZhuchkaTriplesix]

Summary

Fixes #1005: SqliteConnection.inferQueryColumns probes zero-row queries by wrapping the user's SQL in CREATE TEMP VIEW ... AS <sql> via Database.execute, which (unlike rawQuery) runs every statement it's given. A query like SELECT * FROM t WHERE 0; DELETE FROM t reaches this path precisely because rawQuery only ran the first statement and got zero rows back — so the probe would then execute the DELETE for real as a "harmless" side effect of inferring column names for the grid.

Fix

Added sqliteHasMultipleStatements (lib/core/database/sqlite_sql.dart), a small string/quoted-identifier/comment-aware scanner that detects a real second statement after a top-level ;. inferQueryColumns now skips the TEMP VIEW probe entirely when the text has more than one statement, falling back to the existing single-table schema lookup instead (which never executes the query text).

Test plan

• Unit tests for sqliteHasMultipleStatements (single statement w/ trailing ;/;;, real second statement, semicolons inside strings/quoted identifiers/comments not counted)
• Regression test reproducing the original bug: confirms a DELETE smuggled after a WHERE 0 no longer runs via inferQueryColumns. Verified this test fails without the fix (temporarily disabled the new check, confirmed the DELETE runs, restored the fix).
• flutter analyze — no issues
• Full flutter test suite (1865 tests) — all passing