Raise error on invalid attributes directly

[pelme]

Currently, invalid attributes (such as integers) gets raised during rendering, not when constructing the element, leading to cryptic stack traces.

The error should be raised directly when constructing the invalid element, not during render:

>>> el = div(a=1)
>>> print(el)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/andreas/code/htpy/htpy/__init__.py", line 272, in __str__
    return _Markup("".join(str(x) for x in self))
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andreas/code/htpy/htpy/__init__.py", line 272, in <genexpr>
    return _Markup("".join(str(x) for x in self))
                          ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andreas/code/htpy/htpy/__init__.py", line 331, in _iter_context
    yield f"<{self._name}{_attrs_string(self._attrs)}>"
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andreas/code/htpy/htpy/__init__.py", line 112, in _attrs_string
    result = " ".join(k if v is True else f'{k}="{v}"' for k, v in _generate_attrs(attrs))
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andreas/code/htpy/htpy/__init__.py", line 112, in <genexpr>
    result = " ".join(k if v is True else f'{k}="{v}"' for k, v in _generate_attrs(attrs))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/andreas/code/htpy/htpy/__init__.py", line 106, in _generate_attrs
    raise ValueError(f"Attribute value must be a string , got {value!r}")
ValueError: Attribute value must be a string , got 1

[pelme]

This is fixed in 24.9.1!