fix: preserve loadFile transaction errors

[huytdps13400]

Summary

• give importSqlFile() one transaction-finalization scope instead of rolling back in nested catches
• rely on RAII to close the input stream
• roll back only after a successful BEGIN and before a successful COMMIT
• preserve file, line, command, and primary SQLite error context
• append rollback failures without masking the original import failure
• add an iOS harness fixture proving rollback and connection reuse

The regression is registered only on iOS because its fixture path is supplied from the bundled iOS example resource. The production fix is shared C++ and was also compiled through the Android app build.

Verification

• focused iOS harness RED before fix: error lacked Could not load file: context
• focused iOS harness GREEN after fix: 1 passed
• full iOS react-native-harness: 3 suites, 69 tests passed
• iOS native app build: succeeded
• Android :app:assembleDebug for arm64-v8a: succeeded
• bun typecheck (all three workspaces)
• Prettier and clang-format checks
• git diff --check
• no lockfile changes

Closes #308.