[rust-compiler] Fix inner function debug log flushing and todo error event format

Fixed 2 test failures: (1) Inner function debug logs were lost when
analyse_functions returned an error because the `?` operator propagated
before logs were flushed. Now captures the result, flushes logs
unconditionally, then propagates. (2) CompilerDiagnostic::todo() produced
nested error events with sub-details while TS uses flat format with loc
directly on the detail. Added flat-format detection in log_error,
compiler_error_to_info, and log_errors_as_events. 1722/1723 passing.