- Validate spans during existing lexer and parser unit tests, and in `enso_parser_debug`.
- Fix lost span info causing failures of updated tests.
# Important Notes
- [x] Output of `parse_all_enso_files.sh` is unchanged since before #7881 (modulo libs changes since then).
- When the parser encounters an input with the first line indented, it now creates a sub-block for lines at than indent level, and emits a syntax error (every indented block must have a parent).
- When the parser encounters a number with a base but no digits (e.g. `0x`), it now emits a `Number` with `None` in the digits field rather than a 0-length digits token.
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