[BugFix] openbb-core: Handle FastAPI 0.155.0 Query json_schema_extra default of None (#7803)

FastAPI 0.155.0 changed the default of Query(...).json_schema_extra from {}
to None. ReferenceGenerator._get_function_signature_info copied that value
and later called .pop() on it, which broke
test_get_function_signature_info_with_query_default and
test_get_function_signature_info_query_default_branch. CI installs the
newest FastAPI because it does not install from uv.lock. Fall back to {},
as the Annotated branch of the same function already does.

Also cover the unclosed-bracket fallbacks in docstring_generator
(_matching_bracket returning -1 and _rewrite_optional_and_union returning
the input unchanged), which no test reached since #7794.

Co-authored-by: dlee-bq <325002271+dlee-bq@users.noreply.github.com>

openbb_platform/core/openbb_core/app/static/package_builder/reference_generator.py

@@ -602,7 +602,7 @@ class ReferenceGenerator:
                     else str(param_type)
                 )
                 description = default.description  # type: ignore
-                json_extra = default.json_schema_extra  # type: ignore
+                json_extra = default.json_schema_extra or {}  # type: ignore
                 has_default = hasattr(default, "default") and default.default not in [
                     Parameter.empty,
                     PydanticUndefined,

openbb_platform/core/tests/app/static/package_builder/test_docstring_generator_helpers.py

@@ -1961,6 +1961,7 @@ def test_literal_choices_reads_bare_optional_and_non_literal_types():
         ("list[typing.Optional[str]]", "list[str | None]"),
         ("<class 'str'>", "str"),
         ("datetime.date", "date"),
+        ("typing.Optional[str", "Optional[str"),
         # Literal still collapses to str; duplicates still collapse
         ("typing.Optional[typing.Literal['a', 'b']]", "str | None"),
         ("typing.Union[typing.Literal['a'], typing.Literal['b']]", "str"),