Fix execProtocolRawSync spin after backend exit

[psh4607]

작업 배경

execProtocolRawSync swallowed exceptions from the Postgres WASM main loop unless they matched the database error longjmp sentinel. When the backend exited or crashed mid-message, the input offsets stopped advancing and the synchronous loop retried forever at 100% CPU.

티켓 및 링크

• GH-1058

작업 내용

• Rethrow ExitStatus, RuntimeError, and other exceptions outside the known longjmp recovery path.
• Preserve the original protocol error when cleanup also fails, while always restoring the host process.exitCode.
• Add bounded child-process regressions for backend exit with and without an open transaction, synthetic runtime failure, cleanup failure, and child cleanup.
• Add a patch changeset for @electric-sql/pglite.

테스트

• pnpm --dir packages/pglite exec vitest run tests/exec-protocol-backend-exit.test.ts tests/exec-protocol.test.ts --reporter=verbose
• pnpm --dir packages/pglite exec vitest run tests/basic.test.ts --testNamePattern='restores process.exitCode' --reporter=verbose
• pnpm --dir packages/pglite typecheck
• pnpm --dir packages/pglite stylecheck