🐛 fix(resolver): bind only what a guarded statement defines

[gaborbernat]

A TYPE_CHECKING statement that fails to execute has its names stood in as forward references, so annotations using them still resolve. Collecting those names walked the statement's whole subtree for Store-context names, which also picks up comprehension, loop and with ... as targets. The module holds no such names at runtime, so binding them created them: a guarded REGISTRY = {type: Dataset[type] for type in (int, str)} put a placeholder under type in the module globals, after which def describe(value: type) resolved to the placeholder in place of the builtin. The parameter rendered as unlinked text, and calling the function in the same process raised TypeError: TypeAliasForwardRef.__call__() takes 1 positional argument but 2 were given. Only the statement's own targets are read now, recursing into the bodies of the statements it wraps. 🧹

The Failed guarded type import warning asked whether the failing statement was an ast.Import or ast.ImportFrom, which misses the shapes guarded imports tend to take:

if TYPE_CHECKING:
    if sys.version_info >= (3, 11):
        from typing import Self
    else:
        from typing_extensions import Self

    try:
        from orjson import Fragment
    except ImportError:
        from json_fallback import Fragment

There the import is a leaf of an ast.If or an ast.Try, so a dependency missing from the docs environment went unreported, and the name binding could not make up for it either, because ast.alias is not an ast.Name. The check now looks for an import anywhere in the statement, restoring the diagnostic #741 asked for. Statements that stay silent leave a _LOGGER.debug line, so a typo in a guard stays traceable with -vv.