Previously, the lexer greedily consumed a `-` followed by a digit as a single negative number token, causing "1 -1" to be lexed as two number tokens instead of a minus operator and a positive literal. This broke parsing of subtraction expressions without spaces.
Now `-` always emits a TOKEN_MINUS, and the parser handles unary negation. This is a breaking change: `-16.sqrt` is now parsed as `-(16.sqrt)` instead of `(-16).sqrt`, requiring parentheses for negative method receivers. All number method tests (abs, ceil, floor, sqrt, toString) are updated to use explicit parentheses for negative receivers.
Rename the IO.write method to IO.print, which now prints without a trailing newline, and add a new IO.print method that appends a newline after output. Update all benchmark, example, and test files to use IO.print instead of IO.write. Additionally, implement Unicode escape sequence parsing in the compiler's string tokenizer, supporting \uXXXX and \u{...} syntax with proper UTF-8 encoding for code points up to U+10FFFF.
Replace the global `io` singleton object with a static `IO` class, moving the `write` native from the instance to the metaclass. Update all benchmark, example, and test files to use `IO.write()` instead of `io.write()`.
- Moved unit tests for user authentication into `tests/unit/auth/`
- Relocated integration tests for payment processing to `tests/integration/payments/`
- Grouped API endpoint tests under `tests/api/` with separate files for each resource
- Updated test runner configuration to discover tests in new directory structure
