mypy findings with traitlets 5.10.1

[bollwyvl]

Downstream on conda-forge, mypy found the following issues when run under the pyproject.toml settings vs traitlets 5.10.1. Of course, some of these might be false positives.

/core/magics/ast_mod.py:244: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
/core/extensions.py:89: error: Item "None" of "Optional[Any]" has no attribute "builtin_trap"  [union-attr]
/terminal/prompts.py:100: error: Item "None" of "Optional[Any]" has no attribute "mime_renderers"  [union-attr]
/terminal/prompts.py:102: error: Item "None" of "Optional[Any]" has no attribute "mime_renderers"  [union-attr]
/core/formatters.py:56: error: Need type annotation for "ipython_display_formatter"  [var-annotated]
/core/formatters.py:61: error: Need type annotation for "mimebundle_formatter"  [var-annotated]
/core/interactiveshell.py:1785: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
/core/interactiveshell.py:2380: error: Item "None" of "Optional[Any]" has no attribute "lazy_magics"  [union-attr]
/core/interactiveshell.py:2403: error: Item "None" of "Optional[Any]" has no attribute "lazy_magics"  [union-attr]
/core/interactiveshell.py:2431: error: Item "None" of "Optional[Any]" has no attribute "__enter__"  [union-attr]
/core/interactiveshell.py:2431: error: Item "None" of "Optional[Any]" has no attribute "__exit__"  [union-attr]
/core/interactiveshell.py:3184: error: Incompatible types in assignment (expression has type "int", variable has type "None")  [assignment]
/core/interactiveshell.py:3232: error: Item "None" of "Optional[Any]" has no attribute "store_inputs"  [union-attr]
/core/interactiveshell.py:3246: error: "object" not callable  [operator]
/core/interactiveshell.py:3250: error: Item "None" of "Optional[Any]" has no attribute "__enter__"  [union-attr]
/core/interactiveshell.py:3250: error: Item "None" of "Optional[Any]" has no attribute "__exit__"  [union-attr]
/core/interactiveshell.py:3253: error: Item "None" of "Optional[Any]" has no attribute "__enter__"  [union-attr]
/core/interactiveshell.py:3253: error: Item "None" of "Optional[Any]" has no attribute "__exit__"  [union-attr]
/core/interactiveshell.py:3297: error: Item "None" of "Optional[Any]" has no attribute "store_output"  [union-attr]

We'll skip and ship anyhow, but wanted to note this someplace more visible.