Parser doesn't properly handle non-BMP characters

[robbie01]

It seems like the parser isn't properly handling a UTF-16 surrogate pair and tries to create an illegal character.

This precludes the use of the hy package (which implements the Hy language). It includes some exotic characters to test if a specific behavior of ast.parse occurs.

Traceback (most recent call last):
  File "/home/robbie/bookshelf/main.py", line 1, in <module>
    import hy, hy_main # type: ignore
  File "/home/robbie/bookshelf/.venv/lib/python3.11/site-packages/hy/__init__.py", line 11, in <module>
    import hy.importer  # NOQA
  File "/home/robbie/bookshelf/.venv/lib/python3.11/site-packages/hy/importer.py", line 13, in <module>
    from hy.compiler import hy_compile
  File "/home/robbie/bookshelf/.venv/lib/python3.11/site-packages/hy/compiler.py", line 14, in <module>
    from hy.errors import HyCompileError, HyLanguageError, HySyntaxError
  File "/home/robbie/bookshelf/.venv/lib/python3.11/site-packages/hy/errors.py", line 9, in <module>
    from hy.compat import PYPY, PY3_13
  File "/home/robbie/bookshelf/.venv/lib/python3.11/site-packages/hy/compat.py", line 22, in <module>
    if "def" in ast.unparse(ast.parse("𝕕𝕖𝕗 = 1")):
  File "/home/robbie/graalpy-24.2.1-linux-amd64/lib/python3.11/ast.py", line 50, in parse
    return compile(source, filename, mode, flags,
  File "<unknown>", line 1
    𝕕𝕖𝕗 = 1
    ^
SyntaxError: invalid character '\udd55' (U+DD55)

[msimacek]

I tried to run hy's tests and I made a fix for this and few other things. I got the tests to pass 597 out of 609 tests. The REPL works, although readline support is limited (no autocomplete etc.). PR in #500